Friday, November 30, 2007

Winter Storm: Dec. 1-2 -- Final Forecast & Links

Final Forecast: Models tonight still in astounding agreement with not only total precip, but even timing. Low pressure track is still slightly variable, however the warm air and its' progress seems to be in fairly good alignment. Given this case, will still likely side towards the WRF and its' solution given it has better resolution for the shallow warm layers that will take place. The GFS has also been extremely aggressive with warm air advection; and seemingly trying to pull near 60 degree temps into southern Iowa. That is not likely to happen and thus makes me lean a little more away from that kind of solution...

Looking at model initialization, current surface plots have the low at 998mb along the WY/CO border; neither model has anything close to that. Pressure falls currently show strong tendencies of moving this low to the east or northeast; potentially this storm moving a big quicker? Or further north compared to model forecasts? This is going to be very hard to tell and will likely just need to be watched to see what takes place. Either way, need to make a forecast off of it:

Essentially for my final forecast I'm going to list some cities and make the detailed forecast for them. In the end we can see how close I came, others in the area reading this can make comments as well to let me know how close I came. Once again, areas north of highway 30 under a Winter Storm Warning while areas along and south in an Ice Storm Warning.

Sioux Falls, SD: Precipitation likely beginning ~7 AM in the morning as snow, snow should last throughout the afternoon hours with some moderate to heavy snow possible. By mid-afternoon however, some sleet and/or ice pellets may begin to fall with accumulations possible. Snow totals of 4-7 inches & up to another quarter of an inch of sleet/ice pellets and possibly freezing rain before the storm winds down Saturday night.

Sioux City, IA: Snow beginning by 7 AM as well here, however this will be changing over to freezing rain by Noon and to rain by Saturday evening; a couple hours of rain may then switch back over to freezing rain and a bit more snow by Sunday morning. Total snow accumulation of 2-5", freezing rain and IP/sleet accumulation of a quarter of an inch.

Omaha, NE: Beginning as freezing rain from the beginning on Saturday morning, however changing over to rain just before Noon. Likely to stay as rain, with maybe a final glaze of ice before the storm ends Saturday night. Total ice accumulation of a third to half an inch; liquid rain near another third to half an inch.

Spencer, IA: Snow during the morning hours, turning over to ice pellets/sleet during the early afternoon hours with the potential for freezing rain as well into the evening. A light snow may occur before the storm ends Saturday night; total snow accumulation of 3-5 inches with ice/sleet accumulations of over a half inch possible.

Carroll, IA: Ice pellets or sleet to begin in the morning, turning to freezing rain and then rain during the early afternoon hours. Rain may likely finish this storm off, a few sleet or ice pellets may accompany it however. Around a half inch of some form of frozen precip; another half inch of liquid rain possible.

Creston, IA: Freezing rain turning to rain is the story once again, up to 6 hours of freezing rain before the rain in the afternoon. Around a third of an inch of ice, followed by ~.5 inches of rain.

Mason City, IA: Snow in the morning hours turning to freezing rain before Noon; some rain seems possible although dependent on ground and ice temp as well as the rain it may just freeze on the surface as well. Total ice accumulation of a half inch to two-thirds of an inch; a tenth of an inch of other forms of precipitation (rain, ice pellts & sleet).

Ames, IA: A bit of snow before freezing rain begins in the morning, the switch to rain seems to occur around supper-time. Rain likely throughout the nighttime hours with total liquid rain totals of a quarter to third of an inch. Ice accumulation of near a half inch with some accumulation of snow and/or ice pellets as well.

Des Moines, IA: Much the same as Ames, with a bit of snow followed by several hours of freezing rain. Rain change over seems to occur in the late afternoon, total rain accumulation of a third to half inch. Total ice accumulation between a third and half inch as well.

Ottumwa, IA: Some snow, ice pellets/sleet then freezing rain by Noon, holding off the rain until mid-afternoon. Near a half an inch of frozen precipitation, a quarter to third of an inch of rain with precip ending around sunrise Sunday.

LaCrosse, WI: Snowfall likely by Noon tomorrow, turning to ice pellets/sleet by evening and some rain by the overnight. Total snow accumulation of 2-5 inches, ice accumulations up to a half inch; various other frozen precip types may total up to another quarter of an inch.

Waterloo, IA: Some snow or ice pellets during the late morning hours before freezing rain takes over for the afternoon/evening. Rain may work its' way in during the overnight, rain total near a tenth of an inch. Ice accumulations may be hefty, looking at a half inch to near three-quarters of an inch. Snowfall accumulation likely an inch or less by the time the storm ends Sunday morning.

Dubuque, IA: Saturday afternoon expect ice pellets or sleet turning to freezing rain for a majority of the time. Some rain likely to mix in during the overnight hours, totaling a quarter of an inch. Ice accumulations over a half inch seem likely, with near three-quarters of an inch possible!

Davenport, IA: Snow to freezing rain expected by Noon, holding off any precip type change until sunset when it turns over to rain. Expect light rain to occur for much of the night, finishing off Sunday afternoon with a small shot at frz rain or snow. Total ice accumulation of near or over a half an inch possible, rainfall near a quarter of an inch.

Cedar Rapids, IA: The mix of snow/ice and sleet for the late morning and early afternoon, likely staying freezing rain until later afternoon. A total of a half inch or higher of ice accumulation; approx. a quarter inch of rain as things come to an end by Noon on Sunday.

Burlington, IA: Early snow before turning to freezing rain by Noon on Saturday, likely to stay that way until later afternoon. Total ice accumulation of a quarter to third of an inch; rain totals near a quarter of an inch as well. Precipitation likely to taper off by Sunday afternoon.

Updates likely throughout the day tomorrow as I receive information and check out the current conditions around the state. Be sure to check road conditions and the latest updates on your forecast before heading out anywhere, I'm sure by the afternoon tomorrow that travel will not be advised. First potentially dangerous winter storms, with all the makings for possible widespread damage if conditions do fall into place.


8:45 PM Update: I've updated the frame on the right of the blog posts to contain several links that may be of interest to people within this storm. The Surface Plots are simply a map that has the plots for the weather stations, information shown include winds, temperature/dewpoints and current weather with cloud cover. The Iowa Road Conditions is just that, the current road conditions for the state of Iowa as updated by the Iowa DOT. The IEM Freeze is an exceptionally good tool for freezing rain conditions, it overlays the current radar image with air temperatures (numbers) and pavement temperatures (dots). The Iowa weather round-up is a text version of the station plots in case you would like to read instead of interpret. The Iowa Watches/Warnings/Advisories link contains the texts to all of the issuances for Des Moines NWS and all surrounding, please search your county name to find ones of interest. Lastly, local storm reports will be updated by the NWS offices as they receive them during the storm; NWS office codes are within parentheses.

Winter Storm: Dec. 1-2 -- Update #4

5:15 PM Update: The remainder of NWS offices have now upgraded the watches to warnings, as expected for Iowa areas along & south of Highway 30 for a majority are under an Ice Storm Warning. Areas to the north of their are under a Winter Storm Warning; areas under the winter storm warnings are likely not only to receive decent snowfall amounts, but also significant icing. Current forecasts continue to indicate that snow will begin for areas along and north of highway 30 during the morning hours tomorrow, by early afternoon changing over to freezing rain. Total snow accumulations ranging from 1 inch near highway 30 to near 6 inches along the IA/MN borders. Ice accumulations following may reach upwards of one-half inch, making conditions over the area quite treacherous. For the areas south of highway 30 and currently under an ice storm warning, freezing rain is expected to begin by the morning hours tomorrow; beginning its' transition to mainly rain by noon in extreme southern Iowa or by mid-afternoon near highway 30. Up to an half inch of ice is possible before transitioning to mainly rain. Any areas across the state may see sleet or ice pellets occasionally as precipitation types change over.

A detailed, city by city forecast will likely be produced tonight after the 00z model runs. This will be my final call for this event that may be one of the worst initial winter storms in some time...


3:15 PM: The Winter Storm Watches are now starting to be turned over into various warnings across the plains states. I'll list off some of the general areas of where the new warnings are, you can click on the link to read through the latest warnings of those types. You may have to search for your local NWS office and their list, the easiest way to find your latest warning may be to use the search function and type in your county name.

Areas of KS/MO/IL have been put under a Freezing Rain Advisory.

Just north of that over portions of northern KS, southern NE, northern MO, southern IA and into central IL are now listed under an Ice Storm Warning.

Winter Storm Warnings are likely to replace the watches to the north of the freezing rain advisories/warnings. Currently areas of WI/MI/MN and Iowa have been listed under these, with more areas likely to come.

Snow Advisory for portions of northern MN also now issued.

Not all NWS offices have issued their warnings yet, currently the offices yet to upgrade the watch include LaCrosse, WI; Des Moines, IA; Sioux Falls, SD; Minneapolis, MN; Aberdeen, SD; North Platte, NE. These offices are likely to issue upgrades within the next several hours. A new forecast update will be available by midnight tonight in my next blog post. At that time I will once again cover all of the warnings that are currently issued for Iowa and the surrounding area.

Thursday, November 29, 2007

Winter Storm: Dec. 1-2 -- Update #3

Winter Storm Watches are still the only issuances that have been made by the NWS thus far, don't expect any of them to change over until tomorrow afternoon when areas of KS and possibly NE may see the upgrade as the storm begins to affect them by early Saturday. Early Saturday morning is when we will likely see a majority of the warnings come out, likely ranging from heavy snow warnings in SD/MN to winter storm warnings and freezing rain advisories over portions of IA/MO and areas to the northeast.

The afternoon runs of the WRF & GFS became a little closer together, timing is still an issue as the GFS is more progressive. Currently belief is that the WRF, although an outlier with the other models may actually have the best idea of what is occurring near the surface; due to the model resolution. Both are fairly similar in total precip amounts over the plains states as of the 18z runs. The 00z run (tonights) of the WRF has just came in and it has kept fairly consistent on most grounds, it actually increased the total precip amounts over NE/IA/MN. No substantial differences in its' temperatures at the different levels between the runs either. Will have to wait and see how the GFS handles things with its' 00z run.

Ended up not having a lot of time for a detailed forecast, but here is my quickcast for this weekend in Iowa. Both the WRF & GFS are fairly warm now over the state of Iowa, giving way to a mix of snow, freezing rain and even general rain showers. Areas of extreme northern Iowa look to receive the heaviest snow amounts, but likely only in the 4-7" rain at the maximum. They will likely see some sleet and freezing rain by Saturday evening, thus hampering the snowfall totals. Much of the rest of Iowa may see snow beginning on Saturday, but by evening have freezing rain or rain falling as temperatures continue to rise just above the surface. Some areas in extreme southern Iowa may get away with mainly freezing rain and rain, snow being the least prominent precip type.

The forecast is still going to be quite tricky, as the strength of warm air advection just above the surface is crucial to what type of precip is going to fall. The exact path of the low pressure system is also going to have some affect, a more southerly track than currently forecasted will bring more snow to northern Iowa as not as much warm air is likely. I'll likely get one more quick forecast in tomorrow afternoon, likely with updates on what types of warnings/advisories are going to be issued for the state.

Winter Storm: Dec. 1-2 -- Update #2

Winter Storm Watches have been issued from the CO/KS borders through eastern NE and covering portions of MO/IA/SD/MN/WI and IL. Areas under the watch can expect severe winter conditions to become possible within the next 48 hours, potential for heavy snows, freezing rain accumulations along with other types of winter precip. This is a very difficult forecasting situation, with such a strong gradient between receiving heavy snows and substantial amounts of freezing rain. To read the latest Winter Storm Watch texts, please head to this Link; You will have to search for your nearest NWS office and read their watch for your area.

Current forecasts seem to have pushed the all snow line further to the north than my forecast last night, indicating that only areas of SD/MN may receive all snow. All areas of Iowa seem likely to receive more than one precip type from this event. Northern Iowa mainly snow, but some freezing rain/sleet possible, the central and southern two-thirds of the state are all currently included in 'moderate risk' of seeing a quarter of an inch or greater amounts of freezing rain. This is a large concern and could very well become reality. Another complete forecast update will once again come later tonight.

Wednesday, November 28, 2007

Winter Storm: Dec. 1-2

A portion of Iowa got to see a hint at winter last week just before Thanksgiving, with mainly areas of snow falling over southcentral and eastern Iowa. Up to 5 inches had fell with that quick storm, all of it melting in a matter of days. This next system looks to give the entire state a shot at some impressive amounts of precipitation, worse is that it is all not likely to fall as the same type of precip. Currently the two main weather models for forecasting, the WRF & the GFS have some fairly significant differences. The WRF wants to be stubborn with the upper level wave that is likely to aid in the development of a lee of the rockies low pressure system; keeping it further west than the GFS. The difference in timing is ~6 hours and location wise, the WRF is ~150 miles further south with the strongest QPF (precip). Besides the timing and location, which are two important things obviously; the amount and locations in terms of levels within the atmosphere are going to be very important for this event.

The WRF and GFS are in agreement for some locations for the type of precip at the beginning of the system. However, the GFS is much more aggressive with the low pressure system and thus the warm air advection. This ends up transitioning the event from snow, to sleet and possibly freezing rain and even to straight rain in some areas. This is another conflict that the models are currently having and making forecasting a little trickier, although current consensus is leaning towards agreement with the GFS. Thus, the following forecast for the sections of Iowa:

Northwest: Mainly snow event, although some sleet & other types of frozen precip can't be rules out. Potential will exist for some very heavy snow amounts, current model forecasts are for 8-12". Timing looks to be from Saturday morning tapering off into Sunday evening.

North-central: Another mainly snow event, although a little better chance for some sleet by Sunday afternoon. Snow amounts between 5-9" seem possible in this area, beginning Saturday Noon and lasting into Sunday.

Northeast: Snow seems likely to begin by early afternoon on Saturday, potentially changing over to sleet and even rain by Sunday. Snow amounts between 4-7" are possible, although any rainfall could dramatically decrease that amount due to melting.

Southwest: Areas of southwest Iowa are going to be in a harsh area of winter weather in models are correct, with snow and substantial freezing rain and finishing off with cold rain. Snow forecasts are still 6-9", but lower amounts of snow and higher freezing rain amounts are likely as well. This is a very tricky area of forecasting, and will likely fluctuate up until the actual event.

South-central: Another area that will likely be along the lines of heavy snow, freezing rain and a complete turn-over to a cold rain. Snow forecasts are still indicating 4-7", but once again with a tenth or two of freezing rain also possible the snow amounts could be dramatically different. Rainfall after the snow/frz rain could also aid in actually helping the situation by melting, although it could also create an even worse environment. Once again another area that is going to be in a forecast fluctuation up until the event.

Southeast: Snowfall, freezing rain and rain all seem possible for this area of the state. Snowfall amounts within the range of 3-6" seem possible, but freezing rain also possible as well as rain over portions of the state could likely reduce that amount. Saturday afternoon snowfall with the precipitation tapering off by Sunday evening seem the likely timing.

Forecasts will likely be revived each night as the event nears, each model run could likely change the type of precipitation expected due to the 'touchy' nature of the system and the temperatures affects of precip type. By tomorrow night there may be some type of winter storm watches out for the state, it has been mentioned by the NWS offices that cover the state. With tomorrow's update I will post any information on those watches if they have been issued, or with information on when they will be issued. A tricky event that could be potentially dangerous to any travelers this weekend across the state..

Winter Storm: Round 2

A strong and potent storm system has its' sights on the plains for this weekend, the potential is there for portions of Iowa to receive some hefty snow amounts, along with the potential for sleet and freezing rain; even just plain rain for some areas. A complete forecast of this system with more details on where the worst weather may be will be posted by tonight. Keep checking back for updates, as winter looks to arrive once again!

EDIT: Complete Forecast Coming ~11PM

Thursday, November 22, 2007

First Snowfall of the Season

A day before Thanksgiving, hampering travel plans or allowing some to see a white Thanksgiving for the first time for quite a while. Previous years have struggled to accumulate November snow and actually keep it on the ground for a while into the holidays. However this year portions of the state were able to add on the snow pack right on time for the holiday travelers over portions of Iowa. Needless to say with less than 24 hours before Thanksgiving day it was going to have no problem sticking around for the holiday.

This snowfall was actually setup to the north of the surface low pressure system and a ways north of any actual frontal boundary. The cold front with this system was draped from southern Missouri through Arkansas and back into eastern Texas, a stationary front was located from central to northeast Missouri and then through central Illinois and further to the northeast. However, a jet streak over the Great Lakes and one over the Central Plains allowed for a favorable region for strong divergence aloft and therefore upward motion occurring over portion of Iowa and small portions of the surrounding states. The best snowfall occurred just before Noon yesterday and into the early afternoon hours in central Iowa; eastern Iowa saw the snow begin in the early afternoon hours and continue into the early nighttime hours.

Forecasted snowfall amounts were in the 2-5 inch range, as Snow Advisories were issued Tuesday night for portions of southeast Iowa. Wednesday morning these advisories were expanded further to the northwest, then including areas of Ames & Des Moines as well as Cedar Falls/Waterloo area. This event was seemingly well forecasted, mainly given the timing of snow which was centered over times when a lot of holiday travel is occurring. Accumulated snowfall extended as far northwest as Fort Dodge (dusting) and as far west as Jefferson (dusting); northward extent included areas of Waterloo (1 inch) eastward into Illinois. The rain/snow line was featured from extreme northwest Illinois, nearly along the Mississippi River valley and into extreme southeastern Iowa into the northeast corner of Missouri. Areas to the north and west of that line received the snow amounts, while other areas west and south saw mainly rain and a few snow flurries.

Heaviest amounts of snow came in patches, one around the Des Moines area and the others to the west of Iowa City & Cedar Rapids along with another patch northeast of there. 5.2 inches was the high amount of the day, this reported 2 miles southwest of Clive; a 4.8 inch amount was not far behind and it came from the airport in Des Moines. Other areas around Des Moines received snowfall amounts in the 3-4 inch range, Ames only received an inch of snow however as the gradient really dropped off the amounts as you went outside of the bands that occurred. Out of the Davenport NWS office, 4.5 inches in Norway, IA was the high amounts; 4.2 inches near Manchester and 4 inches in Delaware. Cedar Rapids had 2.3 inches accumulated, Davenport NWS office received 0.2 inches.

Check out the Co-op Observers map for all of the snowfall reports across the state from yesterday. Have a Happy Thanksgiving!

Thursday, November 15, 2007

Fall Break Begins

Most colleges are going to begin their fall break over the next week for the Thanksgiving holiday, some are getting the latter part of the week off while others are getting the whole week. Iowa State gets the whole week off next week, before returning for one more week of classes, followed by 'dead week' and then finals. So the semester is winding down, which is a good sign that we should be seeing some of the warm air disappearing. This weekend shouldn't be too bad, but looking ahead into the holiday it looks like the cold air will make its' way into the state. Maybe some wintery precip to come with it?!

Before we get to that cold air, we'll deal with some fairly average temperatures. Lows tonight in the mid 20s to lower 30s, highs tomorrow will actually rise above normal for a majority of the state; upper 40s in the northeast to near 60 in the west. Low to mid 30s for Friday night followed by some cooler highs on Saturday, mid 40s to lower 50s from north to south. Lows remain close to the same on Saturday night, mid 20s to lower 30s; Highs on Sunday in the mid 40s to mid 50s from northeast to southwest. A weak wave may move in during the day on Sunday, giving a small chance at some clouds and sprinkles over the state; mainly north. Those clouds stick around to leave temperatures a bit warmer Sunday night, lows in the mid 30s to near 40 across Iowa.

By next week the situation gets a bit more interesting, with weather models beginning to diverge on solutions. A low pressure system may begin to develop to the southwest of the state, leading a warm front to form just to the south of the state. This will put the state in a favorable position for precip beginning on Monday night and potentially lasting through Thanksgiving! The forecast is very tricky, as the warm front will lead to warm air overrunning the state and providing some fairly steady rains. However, depending on the low pressure track and to whether it goes south of the state or even forms at all will decide how long the rain continues. Not to mention, if the low can to the south and/or east of the state we may see the finale of the storm put down some snow amounts. Weather is quite a touchy subject to forecast this far out, so no promises are being made as to how this will turn out. Just keep checking back early next week for more information on the possibilities of snowfall.

Wednesday, November 14, 2007

Very Windy!

A majority of the state is under Wind Advisories through the next couple of hours, and have been previously since this morning. A strong cold front has moved through the state and a tight pressure gradient along with it has whipped up these northwesterly winds to speeds up to 50 mph. Since this morning, over 30 weather stations across the state have had a wind gust over 40 mph. This number is increasing as over the past hours the winds have really increased, currently at my station near Terril, IA the wind gusts have been the highest of the day with measured gusts of 44 and 46 mph on separate occasions.

These winds should decrease as the sun sets, although a blustery night is still in store the winds should stay below 30 mph. These winds will help the temperatures from dipping down into the teens as they mix the air throughout the lower atmosphere. However, this still cold temperatures combined with that much wind will still make it feel like temperatures in the teens or lower.

Breezing conditions still exist for Thursday, but at least the sun should be shining. Expect conditions to calm and the temperatures level off in the mid 40s to mid 50s over the state by Friday and continue through the weekend.

Tuesday, November 13, 2007

One last mild day...

After a surge of warm air came into the state early Sunday morning it has left us with temperatures that have been above normal and felt pretty good for this time of year. Today looks to be the last day with those conditions with the highs ranging from the mid 60s to near 60 across the state. Lows tonight will represent the movement of the cold air into the state nicely, mid 30s in the northwest to the mid 40s in southeast Iowa. This colder air should be in place pretty well by tomorrow, highs ranging from the upper 40s to the mid 50s from northwest to southeast as well.

The latter portion of the week will feature highs in the mid to upper 40s on Thursday, warming slightly to the mid 40s to mid 50s as warm air beings to move into the Missouri valley. Lows will drop below freezing for a significant portion of the night on Wednesday & Thursday, with lows in the mid to upper 20s. Friday night has lows warming slightly as the warm air continues from the south, upper 20s to mid 30s over the state.

Wondering when that first good snow storm is going to be? Well a rough look ahead at weather models indicate that another cold shot of air is going to make its' way into the state midweek next week. Hard to say whether or not this will give anybody some flakes, for the most part the cold air is behind the system and thus not much for precip. A long shot may put our first snowfall for a majority of the state in the Nov. 25 to Nov. 28 range. Keep in mind that this is a very rough forecast, but I'll keep an eye on things to see how they progress as the possible event nears.