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Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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523 FXUS63 KDMX 080539 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1239 AM CDT Mon Jul 8 2024 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - Scattered showers/storms Nearly Every Day this week. Some with locally heavy rainfall this evening; marginal severe this evening - Seasonal Temps Through Next Friday - Western Ridge Builds East Late in Period with temperatures heating up into the 90s by Saturday && .DISCUSSION... Issued at 202 PM CDT Sun Jul 7 2024 .Short Term /Tonight through Monday Night/... Confidence Short Term: Medium to High Relatively weak flow continues with tropical airmass in place. We continue to see a slowly moving large surface trough over the Northern Plains with an upper level reflection stretching from the Northern Plains south into the Southern Plains. A large subtropical high situated in the Antilles and stretching northeast into the southeast US continues to provide a constant deep moisture plume of +15C dewpoints north into Iowa. The northern extent of the +15C is just at the border at 12z. Within the elongated upper level trough, several weak short waves southwest of Iowa will track into the region within the next 24 hours. This and an approaching cool front will be enough to create another round of showers and storms late this afternoon through tonight. PWATs over the southeast will continue to range from 1.5 to 1.75 in later this afternoon and tonight. Warm cloud depths are holding around 11kft. All combined, we have another late afternoon and evening of tropical rain and with relatively modest steering currents of 20 to 25 kts aloft, will be susceptible to isolated, but locally heavy rainfall amounts in excess of 2 to 3 inches. Though BWD is relatively weak early this evening under 20kts, later in the night along the trailing boundary, BWD increases to 30 to 35kts. This evening we will likely see some pulse storms with wind and some hail potential and later in the night, some organization is possible later in the evening for a short period of time prior to 05z. After midnight, instability will be weakening enough to allow storms to lessen in intensity. By tomorrow evening, the main trough will be exiting the area. We will still have some lingering showers and possible isolated storms mainly east of I35 on Monday prior to 00z. Tomorrow night will quiet down with partly cloudy skies and some fog expected. Tonight and Monday night mins will be rather mild again with overnight lows around 60 northwest to the mid 60s southeast. Monday will be similar to today with highs in the upper 70s to lower 80s. .Long Term /Tuesday through Sunday/... Confidence: Medium to High By Tuesday we will be under the influence of weak high pressure. The remnants of Beryl will be drifting north northeast into the mid Mississippi River Valley. At this time, there is general consensus that the old tropical system will remain far enough southeast of Iowa to not directly influence our weather with any precipitation. Though the GFS/GEFs suite is indicating otherwise, the bias of the GFS suite is likely resulting in a suspect solution. The EPS/EC system keeps the core of the ex-tropical tracking from northeast AR to northeast Indiana by 18z Wednesday. A widespread 2 to 4 inches of rain is expected along its track and thankfully will not impact our area with any more rainfall. Despite this, the one thing that will happen is a weak phasing of the old tropical system with a lingering weak trough in the current northwest flow. As indicated by some of the models, a subtle amount of falling heights Tuesday afternoon, along with daytime heating and expected instability, may be enough to produce a few showers/iso storms over northern Iowa. Wednesday into Thursday a similar weak trough tracks along the western fringes of old Beryl and across Iowa, bringing some airmass showers and thunderstorms to the region during the afternoon and early evening. At this time, it appears that the better chances will be Wednesday with the stronger H500 trough. Thursday will be warm and continued humid, but with lesser afternoon chances for any rain. By Friday, the weak high we had hoped would keep us rain free the previous few days will be moving east. Subtle warm air advection will arrive later Friday afternoon. This will be enough to bring some small thunder chances into the region once again. Highs during the period Tuesday through Thursday will remain in the lower to mid 80s with lows in the lower to mid 60s. Looking ahead to the weekend, the one consistent signal for Iowa will be rapidly warming temperatures back to the 90s. There remains a consistent signal for the western ridge to build east during the period. h850 temperatures are forecast to rise into the lower to mid 20s. This will likely propel highs into the lower to mid 90s. Late in the period a lazy east to west boundary will set up over northern Iowa or southern Minnesota. South of the boundary will be capped with H700 temperatures from 12 to 14C. At this time, the GFS/GEFS/EPS solutions support the front remaining farther north into southern to central Minnesota. This should keep the region dry over the weekend with heat now becoming the main concern. Heat indices should rise to the lower 90s east Saturday to mid to upper 90s central to west Saturday and to the mid 90s to around 100 on Sunday. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1239 AM CDT Mon Jul 8 2024 Convection will depart early this morning from eastern areas with mostly VFR conditions. However, some fog is likely to develop which may lead to MVFR conditions at some terminals toward sunrise. On Monday, generally widespread VFR conditions are expected although isolated showers in the north will produce MVFR conditions in and around the showers. Surface winds are generally light from the south becoming west to northwest by the end of the period. && .DMX WATCHES/WARNINGS/ADVISORIES...None. && $$ DISCUSSION...REV AVIATION...Cogil