Sunrise 6:03 AM   Sunset 8:14 PM Moonrise 2:52 AM   Moonset 2:01 PM

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FXUS63 KDMX 030812 AFDDMX

Area Forecast Discussion National Weather Service Des Moines IA 312 AM CDT Fri May 3 2024

KEY MESSAGES

- Early Morning Fog...Patchy to Areas Dense Fog through 8am - Showers & Storms Tonight and early Saturday || Dry Sunday - Storms Return Monday Evening With Some Severe Risk - Sun/Cloud Mix with passing Showers Much of Next Week; Turning Cooler by weeks end.

DISCUSSION
Issued at 312 AM CDT Fri May 3 2024

Short Term /Today through Saturday/

Confidence Short Term: Medium to High

Active weather pattern for much of the seven day period, though we may luck out a few days next week with precipitation south/north of us. Rainfall is still needed in some areas, but not the southeast.
The filling low that brought the moderate to heavy rainfall to the region yesterday has now migrated to the far Northern Plains. We had a front at H850 still over the eastern counties of the state at 00z, but that has now edged east a bit since then. Another weak area of low pressure is located near Springfield, MO at H850 with a third area of low pressure in northern New Mexico. The Gulf moisture stream has temporarily been pushed south of our area. However, a large plume of +10C to +15C dew points is just south of the region at this time. Meanwhile a weak ridge of high pressure will cool the boundary layer through early morning. Weak winds and ample boundary layer moisture from yesterdays rainfall continue to promote fog development. This will likely peak around 5 to 7 am over the area.
Have updated the grids for areas of fog into the morning commute and will address conditions with either an SPS or maybe an advisory if it looks more problematic before 4 am. After the fog burns off, we will be rewarded with a rather pleasant day to round out an active week. Highs today with patchy fair weather cumulus will reach the lower to mid 70s as south southeast winds increase to 10 to 15 mph by mid to late afternoon. Tonight a wave currently showing up on water vapor imagery over Colorado/Idaho will track east. This will pull an area of low pressure and front east. At the same time, the moisture plume to our south will be pulled back northeast overnight.
PWATs again increase to around 1.25 inches and warm cloud depths increase to over 10kft again from 06z to 18z Saturday. The models continue to indicate the main forcing at H700/H500 will peak from 06z to 12z across the area. As the wave reaches to near the IA MN border and the LLJ weakens significantly overnight, the showers and storms will weaken with time from 06z to 12z. Lesser rainfall is anticipated in the southeast, with amounts northwest of there from .75 to 1.5 inches and in the southeast about a quarter inch. Severe weather chances tonight are not high, but the southwest to the south central has some risk of an isolated stronger storm with a small risk of wind/hail. Shear is just strong enough for some rotation.
Lows tonight will fall to the mid 40s northwest to the mid 50s in the far south. The lingering showers and isolated storms early tomorrow will generally exit the east by mid afternoon as high pressure builds south and east from the Northern Plains. We will be fighting lingering clouds in the afternoon mixed with some peaks of sunshine. Highs will reach the lower 60s northwest to the lower 70s southeast.

Long Term /Saturday Night through Thursday/

Confidence: Medium

Saturday night will be similar to this morning. Clearing skies may lead to some patchy fog once again. We will need to address that on Saturday to see how much dry air is advected southeast into the state. Otherwise, Sunday will be dominated by high pressure slowly drifting east by late afternoon. Other than some fair weather clouds, the day will again be very pleasant. H850 temperatures begin to warm due to return south flow. This will help push highs into the upper 60s to lower 70s by afternoon. We continue to see a southern stream wave in the southeast on Sunday, but there is really no sign of any moisture return across Iowa at that time, so have removed any mention of precipitation. Lows Sunday night dip to the 40s to lower 50s. A large scale trough over the western CONUS will begin to move east on Sunday. This feature has been consistently forecast by the medium range models to form an elongated trough with a double barrel low; one migrating to Alberta and the southern one wrapping up nearer eastern Nebraska. As the entire system deepens and occludes, the southern stream low will pull a wing of moisture/instability into the area later Monday afternoon and into the night. An impressive jet max will increase collocated columnar wind fields from H850 up to H500 by 06z Tuesday over the area. Winds will average 50-65kt through the column with some diffluence at H300.
This, along with enough wind shear and instability to promote some rotation as well as a potential QLCS wind and tornado threat overnight. Obviously, we have several days and some changes may occur. Highs Monday will be mild ahead of the system with 70s across the board. The Euro and GFS are beginning to diverge a bit by Tuesday; GFS faster and the Euro slower. The Euro shows only a quick break early Tuesday from the overnight convection, with another speed max forecast to plow into an area of lingering instability across Iowa. This would tend to promote another area of strong to severe storms over mainly eastern Iowa and states east and northeast of our area. At this time, no solution is favored but the GFS generally trends too fast by days 4 to 5. Will need to remain aware of a second potential round of stronger storms later Tuesday near our area. Tuesdays highs are going to be difficult to nail down for a few days, due to the various solution differences. The most likely range would be the 60s northwest to the 70s southeast. There is some consensus for Wednesday into Thursday with regard to the Northern Plain system evolution. It appears that the large scale system will drift back into the Midwest with more clouds, some passing showers and cooler temperatures by the end of the period. Highs should generally be in the 60s to around 70 by Thursday with 70s still likely on Wednesday. There is some indication that more clouds and cooler conditions will persist late into the week and the following weekend.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
Issued at 1153 PM CDT Thu May 2 2024

IFR/LIFR fog to impact terminals tonight. Lower confidence at KDSM so kept vsbys higher. VFR to resume after 13z with light winds becoming easterly to southeasterly through the daytime hours. Showers and thunderstorms to reach KFOD near the end of the TAF period.

DMX WATCHES/WARNINGS/ADVISORIES
None.

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