Sunday, August 23, 2009

Fall Already?!?

The past couple of days after a cold front passage have definitely had that fall feeling to them, with highs barely into the 70s for much of the state and lows being down into the 50s and even some 40s there in some portions of Iowa. The cool and calm nights led to some dense fog in low lying areas, but perfect nights for sleeping.

We'll begin to warm up today with high temperatures rising into the mid 80s along the Missouri River; and only into the mid 70s along the Mississippi. Low temperatures tonight ranging from the lower 60s to the mid 50s from west to east marking the increase in moisture ahead of our next storm system. Monday's highs will make it to the 80s throughout the state, from the upper 80s to lower 80s from west to east. Moisture will continue to increase across the state ahead of our next storm system, keeping lows in the upper 60s to lower 60s from west to east. We'll see the cold front push through eastern South Dakota and into western Minnesota during the early morning hours on Tuesday, and likely bring showers and thunderstorms to the northern third of the state through the early afternoon hours on Tuesday. While a few severe storms can't be ruled out given sufficient instability and marginal shear, it does not appear to be much more than a marginal wind/hail threat at this time.

Beyond our cold front passage we'll once again see high temperatures in the mid to upper 70s, and a few 80-marks through the remainder of the week. Low temperatures in the mid to upper 50s will make it a bit cooler than normal, but nothing that most will complain about given the nice sleeping conditions.

Tuesday, August 11, 2009

Much Quieter

After a busy weekend for portions of the state we have set into a much quieter pattern for the remainder of the week, with mostly sunny skies and temperatures in the upper 80s and lower 90s across the state. A weak ridge to zonal flow will be in place across much of the western two-thirds of the US through the end of the week. This is what will be leaving Iowa and much of the plains under sunny skies with warm temperatures. As we work into the weekend a trough enters the flow and will begin to affect the northern plains late Friday and continue through Monday. It is still too early to tell the thunderstorm threat, and specifically the severe weather threat with this disturbance.

Enjoy what seems to be the first full week of summer-like temperatures and conditions. Beyond our weekend disturbance long-range forecast models once again bring the jet stream well north and leave the plains in a weak ridge indicative of warm temperatures and mostly sunny afternoons.

A quick look back at Sunday's long lived supercell that progressed along highway 20 throughout the state, the Des Moines NWS has a nice page that shows a radar loop with storm reports. There is also a few pictures that were provided by the Fort Dodge Amateur Radio Association, you can check them out on the NWS page and below:

NWS Des Moines - August 9 Supercell Page

Sunday, August 9, 2009

August 9 Severe Weather Update #1

A morning supercell is moving through portions of central Iowa, currently just west of Fort Dodge capable of producing 1" to 3" diameter hail and damaging winds in excess of 60 mph. This storm has been severe for quite some time this morning, beginning near the Iowa/Nebraska border and moving east/northeast approximately 40 mph.

This storm has a history of producing 1" to 2" diameter hail and damaging winds, creating some blowing hail that has blown out windows of a home near Yetter, Iowa. The strongest part of this storm is expected to effect downtown Fort Dodge and may produce significant hail capable of producing damaging to vehicles, homes, and especially people.

Latest report from Callender indicates at least 60 mph winds, and close to 1" diameter hail that has caused roof damage and tree damage in town.

Friday, August 7, 2009

Severe Weather Potential - August 7 Update #3

Despite the hopes for convection before sunset, it does not appear likely as sunset is within an hour or two and there is not even a watch issued for potential development. Some cumulus is occurring in the warm sector, however, temperatures at 700hPa have increased to 14C directly over the most likely area for development. This is suppressing any chance of convection until at least after sundown across the area...

Thunderstorm development is still possible along the front as the low level jet increases slightly and we see the decoupling of the boundary layer. The tornadic threat with this development will be fairly minimal, with a large hail threat, and a more likely damaging wind threat across portions of southeast South Dakota and then across northern Iowa and southern Minnesota. An additional update is possible, but only if development can actually occur.

Once again Iowa has went and gone off to disappoint the severe weather lovers across the northern plains!

Severe Weather Potential - August 7 Update #2

Convective inhibition remains strong, however, confidence has increased that the inhibition will yield to convection during the late afternoon or evening hours across portions of the warm front in South Dakota and Iowa. Thunderstorms that do develop are likely to be supercellular with the threat for very large hail, damaging winds, and tornadoes given good low level shear and strong instability.

Just a short update... Expect to leave for a chase target in vicinity of Storm Lake, IA in approximately an hour. Storm initiation by 7 PM along the warm front in vicinity of prolonged strong low level convergence that is occurring in this area. Storms should follow this warm front, tapping into strong instability and good shear parameters leading to a continued tornado threat through 9 PM. Eventual evolution to a cluster or linear segments is expected beyond 10 PM with more of a damaging wind threat.

Severe Weather Potential - August 7 Update #1

Not much for changes in the going forecast or in the current analysis of things across the plains states. Watching clearing skies across the Dakotas and Nebraska, which should also work into western Iowa during the early afternoon hours. Warm front currently located along and just east of the Missouri River from South Dakota into western Iowa. This front should slowly move a bit northward, currently inhibited due to cold pool left from cloud cover and showers this morning. Strong instability and good inhibition is still in the forecast for the warm sector through this evening. A shortwave currently over eastern Colorado should move over the corner regions of SD/NE/MN/IA during the evening hours and should provide enough support for the formation of isolated thunderstorms.

Thunderstorms forming along the warm front would appear to be supercellular in nature during the evening hours, with the threat of very large hail, damaging winds, and the potential for a tornado given favorable storm motion. Storms should merge in the early nighttime hours, and begin more of a damaging wind threat across northern Iowa and southern Minnesota. This is confirmed with the latest SPC outlook upgrading the probabilities for damaging winds across this region...

Will watch the warm front evolution, as well as the 700hPa temperatures that will be inhibiting development until the Colorado shortwave makes its' way over during the evening hours.

Severe Weather Threat - August 7

Morning convection continues across southwest Iowa, with additional showers/thunderstorms spread throughout the state and spreading eastward at approximately 30-40 mph. These thunderstorms and showers should continue through the morning hours across much of the state, with cloud cover also remaining through 10 AM across the entire state. Look for a gradual decrease in coverage in both showers and cloud cover through the Noon hour and into the afternoon. Skies should begin to clear from west to east through the Noon hour as well, beginning to leave portions of western Iowa under warm and sunny skies by early afternoon. A warm front currently positioned south of the thunderstorm activity this morning should make its' way northward as the lee cyclone moves out of eastern Colorado and into the plains this afternoon. The warm front should become positioned parallel to I90 across southern Minnesota and likely through South Dakota, with a very warm/moist and unstable air mass to its' south.

Instability values should become quite high (3000-4000 j/kg) given surface temperatures near/above 90 degrees and dew point values well into the 60s and perhaps 70s along/south of the warm front. Strong surface convergence as well as theta-e should be taking place along the warm front, with aid from a subtle disturbance in the mid-levels also arriving during the evening hours across northwest Iowa. The combination of strong instability and continued convergence along the boundary may have the potential to break a cap that is likely to be in place throughout the afternoon south of the warm front. Temperatures at 700hPa are likely to be in the 11-13C range, with temperatures at 850hPa above 20C. Despite the warm temperatures aloft, models continue to indicate surface heating is enough to overcome the cap in areas that have this strong convergence along the warm front.

If the cap is overcome within the warm sector across northwest Iowa or South Dakota, expect rapid intensification of updrafts leading to large hail becoming a likely threat. Given strong shear values, especially for the late evening and early nighttime hours as the low level jet begins to aid the low level flow, a tornadic potential will exist with any development. Expect storms to begin to form into somewhat of a cluster or MCS after 10 PM and continue across the state, with perhaps an additional MCS moving out of the Dakotas and into MN/IA during the nighttime hours. An additional update is likely near the Noon hour, and once again through the afternoon and convective inhibition and the location of boundaries, etc. becomes more defined.

Storm Chasing Status: With a conditional threat, I will likely be sitting in the comfortable confines of home through the afternoon. However, with the threat likely evolving within an hours drive will be watching conditions closely. Current four county target area is Lyon and Osceola counties in northwest Iowa, and Nobles and Rock counties in southwest Minnesota.

Thursday, August 6, 2009

A Few Rounds of Storms

Sunday night did bring a few severe weather reports across the state, mainly of marginally severe hail around an inch in diameter and several wind gusts of 60 mph or so. The wind was strong enough to take down a few trees and power poles in a line roughly along Highway 30 from Sioux City towards Fort Dodge. We've held quiet since then, with temperatures still a little below normal for this time of year.

We'll be able to change the temperature aspect and finally feel some good summer heat and humidity for a few days for this weekend. This will also bring us the conditional chance of some thunderstorms during the late afternoon and overnight hours beginning tonight, and likely lasting through the weekend. At this time it is too conditional to really pinpoint any good chances of a round of thunderstorms, but rather good to mention that if thunderstorms do persist or develop into Iowa they are likely to have a chance of some large hail and damaging winds.

Our first chance will be across western Iowa tonight as a potential MCS will swing by the state coming out of the Dakotas. An additional round of storms may also be coming into northern Iowa by the early morning hours as the threat of an additional MCS seems possible. After these rounds of storms have a chance to move through, a good setup will be featured over portions of SD/MN/IA for severe weather. However, the warm air at the surface will also translate into the mid-levels and may keep us capped from thunderstorms. Sunday also appears to have a chance of thunderstorms, with the likelihood of an upgrade of the severe weather risks issued by the SPC in later outlooks.

While dodging the rounds of thunderstorms, enjoy the warm and humid air as temperature soar into the upper 80s and 90s and dew points rise into the upper 60s and even 70s creating the typical miserable summer feel. Additional updates may be given if warranted...