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Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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826 FXUS63 KMPX 131953 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 253 PM CDT Tue Aug 13 2024 .KEY MESSAGES... - Our dry period ends tomorrow with widespread showers expected to gradually spread west to east tomorrow. The heaviest rain is expected tomorrow evening through early Thursday morning. - Lingering showers are possible Friday & Saturday before we resume our dry and mild stretch by Sunday. && .DISCUSSION... Issued at 252 PM CDT Tue Aug 13 2024 A broad cumulus field has blossomed over the northern plains this afternoon with cumulus evident from southern Canada all the way south through Illinois, Indiana, and Ohio including most of Minnesota & Wisconsin. There are some high clouds moving through southwestern Minnesota as well evident on GOES satellite imagery, with a small chance for a few pop showers much like yesterday in southwestern Minnesota. Light southerly to southeasterly winds continue ahead of the incoming system which will bring showers back to the region tomorrow, alongside a northwesterly wind shift that looks to persist through the next several days. The impetus for initial showers arriving in western Minnesota as early as sunrise tomorrow is a strengthening low level jet bringing an influx of moisture and warmth to force showers as the leading edge of a trough begins to slide eastwards over the northern CONUS Rockies. This jet will continue to pump gulf stream moisture northwards allowing for increasing PWATS into the 1.7-1.9 range which is already a couple tenths of an inch above the 90th percentile for August 14th. A series of shortwave impulses are expected to spread eastwards from the approaching trough which should couple with the jet forcing to produce a large swath of showers and potential storms which will gradually move west to east across Minnesota and into Wisconsin tomorrow. Model guidance has a bit of spread in regards to timing and amount of precipitation with the CAMs favoring a slower onset time and less overall precipitation compared to the medium to long range global models, with significant spread in the GEFS in regards to both total amount of rainfall and the timing. The GEFS mean for MSP would produce an inch and a half of rainfall through 7pm Thursday with a lack of consensus within guidance as most membership spreads from a few tenths to as much as 2 inches. The higher amounts would be possible during the heaviest rainfall which looks to be late tomorrow through around 5-6am Thursday as the low level jet once again strengthens and amplifies the forcing from the trough. The surface response is fairly muted with a surface low only forming as the trough axis swings through by midday Thursday. Overall, expect most of the area to pick up anywhere from 3/4 of an inch to around an inch and a half of rain over a 36 hour period from when precipitation enters the region tomorrow through Thursday. Taking a deeper dive into severe weather parameters, there is also quite a bit of spread in potential as the higher pwats and fairly saturated moisture profile would support heavy rain but only weak storms, especially overnight. As CAM guidance has trended slower than global guidance, the best chance for stronger storms would be near sunrise Thursday with a strong low level jet present alongside increasing instability. As of right now, the main threat would be heavy rain producing outflow or micro-burst type winds, with that threat looking on the lower end of things for now. As the upper level system rotates over the Great Lakes heading into the weekend, further light showers are possible as both aloft and surface winds shift northwesterly, with cold air advection showers possible until the system rotates out further by Sunday. Once we get through Saturday, the rest of the forecast looks dry and a return to what we have been seeing the last week or so, which is mild temperatures and dry weather. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1154 AM CDT Tue Aug 13 2024 Areas of sct`d cu are expected to further develop this afternoon with at least FEW/SCT050 expected, with mainly RWF/MKT having a shot at a BKN cig. Otherwise just high clouds to deal with today amidst dry weather with only a slim chance for a repeat at some isolated showers that developed south of MKT yesterday afternoon. The better chance for showers arrives after the period, with showers slowly moving in tomorrow afternoon and evening. For now, kept the period dry, however based off how CAMs handle the timing we could end up bumping up -SHRA timing to arrive in western MN between 18-21z, MSP by 22-00z, and EAU by 00-02z. Once showers arrive, expect MVFR/IFR to persist through much of Thursday. KMSP...No additional concerns. Left out a mention of -SHRA towards the end of the period with timing looking to be arrival just before 00z right now. /OUTLOOK FOR KMSP/ THU...MVFR/IFR, -SHRA/-TSRA. Wind E to NW 10-15kts. FRI...VFR, chc MVFR/-SHRA. Wind NW 5-10kts. SAT...VFR, chc MVFR/-SHRA. Wind NW 5-10kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ DISCUSSION...TDH AVIATION...TDH