358 FXUS63 KMPX 211149 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 649 AM CDT Sat Aug 21 2021 .UPDATED for 12Z Aviation Discussion... Issued at 645 AM CDT Sat Aug 21 2021 && .SHORT TERM...(Today through Sunday) Issued at 420 AM CDT Sat Aug 21 2021 Today will be a dry and breezy day with increasing clouds in the morning, and clearing skies towards evening. Sunday will start out dry, with chances for thunderstorms spreading from west to east late in the day and overnight. A few storms could be strong to severe with large hail as the primary threat, but the overall set up is rather ordinary. Today and Tonight - A strong surface low will lift northward toward James Bay today, with surface high pressure building in the wake of a passing cold front across the Upper Midwest. The cold air behind this front combined with some boundary layer moisture will lead to scattered cumulus later this morning across the region, but that should dissipate toward evening with deeper mixing and upper level subsidence. Winds will be breezy, out of the west/northwest around 15 mph with gusts near 20 mph. Afternoon highs will be in the low to mid 70s. Overnight, high pressure will build and surface winds will decouple setting the stage for a calm and cool night as lows drop to near 50. Sunday and Sunday night - High pressure will depart eastward, and return flow will set up across the Upper Midwest. This air mass will be only marginally unstable, with highs in the mid to upper 70s and dewpoints in the mid 50s. Couple that with mid level lapse rates of around 7 C/km, and the end result is around 2000 J/kg of MUCAPE. Deep layer shear is quite favorable due to the 90 degrees of veering winds with height between the H925 and H500 levels. For that reason, severe weather does seem possible late Sunday into Sunday night as a shortwave trough approaches from the west. SPC has a marginal risk of severe weather, and the main threat would probably be hail due to the elevated nature of the storms. .LONG TERM...(Sunday night through Friday) Issued at 420 AM CDT Sat Aug 21 2021 Monday is forecast to be dry with clearing skies as surface high pressure and rising 500 mb heights slide through the Northern Plains. Highs will be in the 80s while lows Monday night will be in the upper 50s to mid 60s. Showers and perhaps a thunderstorm may bleed into extreme southern MN Monday night as low-level convergence occurs along the nose of an LLJ in central IA. Highs remain similar Tuesday but forecast models suggest the weather will be more interesting. A shortwave traveling through the Northern High Plains along the International border will create surface cyclogenesis in southeast Manitoba by Tuesday afternoon. A cold front will drape south through the eastern Dakotas while a warm front extends east from west-central MN into WI. Models depict precip developing in the eastern Dakotas/western MN Tuesday morning within a zone of 850 mb moisture convergence north of the warm front. This activity then travels east-southeast, following the instability gradient along the warm front. Should this occur, convection is expected to intensify into Tuesday evening as it encounters MUCAPE of 1500-2500 J/kg (fostered by mid to upper 60s dewpoints) and steep mid-level lapse rates. Additionally, storms should be aided by low-level convergence along the front as a 30 knot southerly LLJ pivots clockwise into Tuesday evening. A few limiting factors about this setup are: 1. Low-level directional and speed shear are quite low. 2. While 50 knots of bulk shear is forecast over western MN, values decrease to 30 knots as one travels east into WI. 3. The southward extent of convection due to the upper-level wave being removed far to the north. This setup will continue to be monitored as there is potential for severe weather on Tuesday, especially during the late afternoon in conjunction with peak heating. Decent model agreement regarding the precip is evident in NBM's PoPs, which are 50-60% along the warm front. In fact, areas that see convection may receive well upwards of an inch (hinted by the 00z ECMWF). As the precipitation pushes east of our area Tuesday night, a cold frontal passage follows Wednesday cooling our temperatures mid-week onward. Highs the remainder of the period will be in the 70s to near 80 while overnight lows will be in the mid 50s to lower 60s. Wednesday looks dry as a surface high slides to the north. However, precip chances return Thursday onward as another broad trough crosses the Intermountain Rockies. While differences between long- range model solutions exist, good agreement is seen in the overall pattern giving support to NBM's PoPs of 40-60% Thursday through Friday night. Looking beyond the period, perhaps our rainfall fortunes may change as zonal flow remains favored over the northern CONUS into early September. EPS members seem to think so with many having QPF of at least 2.5" at MSP over the next 15 days (the highest signal that can be recalled from memory this summer). && .AVIATION...(For the 12Z TAFS through 12Z Sunday morning) Issued at 645 AM CDT Sat Aug 21 2021 VFR/MVFR clouds are expected this morning with breezy west/northwest winds. Later this morning ceilings will lift and clouds will break up, so expect VFR conditions this afternoon and through the rest of the TAF period. Winds will decrease overnight, and become more east/southeasterly toward Sunday morning. KMSP... Could see a few hours of VFR/MVFR clouds this morning with breezy west/northwest winds. Later this morning ceilings will lift and clouds will break up, so expect VFR conditions this afternoon and through the rest of the TAF period. Winds will decrease overnight, and become more easterly late tonight. /OUTLOOK FOR KMSP/ Sun...VFR. Chc TSRA/MVFR late. Wind NW bcmg SE 5-10 kts. Mon...VFR. Wind W 10-15 kts. Tue...VFR. Wind SE 5-10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ SHORT TERM...JRB LONG TERM...CTG AVIATION...JRB