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Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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405 FXUS63 KMPX 141938 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 238 PM CDT Wed Aug 14 2024 .KEY MESSAGES... - Rain increases in coverage this evening, with the bulk of accumulation falling from 7pm tonight through 7am tomorrow. Isolated thunder possible, but storms not expected. - Wrap around showers continue through Friday with dry weather returning this weekend. && .DISCUSSION... Issued at 237 PM CDT Wed Aug 14 2024 Showers have been slow to develop today which coincides with what CAMs were saying yesterday, as opposed to the much more aggressive and widespread global models. The culprit is relatively weak forcing as until now there has been limited shortwave energy within the upper level wave developing the surface low over us, which has kept widespread rain development out of the MPX area and confined to Iowa and the Dakotas. This is expected to remain the case over the next few hours as we await the nocturnal strengthening of the low level jet to bolster the forcing and produce more widespread showers across the area, which looks to arrive after 6-7pm this evening. Forecast soundings continue to point towards little to no instability potential, thus we are not expecting thunderstorms other than the odd rumble of thunder in primarily southern Minnesota as the jet strengthens this evening. The bulk of the precipitation is expected to fall between 7pm to 7am while the jet is strongest, with moisture rich air advecting northwards alongside the low level convergence characteristic of a low level jet. The expected rain amounts have decreased on the high end, with the expected range being 1/2 to 1 inch give or take a 1/4 inch or so depending on where some heavier showers set up overnight. Continued showers are expected on and off throughout Thursday as the upper level low occludes with the surface low spinning over the northern half of the state, with the MPX coverage area with an area of cold air advection aloft on top of relatively warm lower levels. Additional accumulations will only range from a tenth to a quarter inch through Thursday with additional hundredths from more isolated cold air showers on Friday. As the upper level low moves eastwards by mid to late Friday, showers will exit with it as a broad upper level ridge builds over the western CONUS with northwesterly flow alongside general subsidence. Shower chances appear scarce in this setup although we could get a few showers next week with potential shortwave energy drifting through the area on the eastern side of the ridge. Otherwise, expect similar temperatures to the previous couple of weeks with mostly upper 70s to low 80s for highs and diurnal cumulus being the majority of the cloud cover. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1205 PM CDT Wed Aug 14 2024 Most sites will initialize at VFR outside of SW MN sites (KRWF). The main concern this period will be the rain this afternoon through Thursday morning. Rain showers will gradually move NE from SW MN into the Twin Cities and W WI by this evening. A heavier, steady rain will begin after sunset. This will bring the onset of low MVFR and IFR ceilings across the MN TAF sites and WI sites Thursday morning. Continued -SHRA usage for spottier coverage this afternoon and Tuesday morning and -RA for steadier rain overnight. IFR is likely at all sites (outside of EAU until later Tuesday AM) tonight. Lower confidence for any TSRA tonight so I`ve opted to leave it out of the TAFs. We`ll see rain begin to taper off Tuesday morning with a gradual improvement of cig/vsbys by the end of the TAF period. KMSP... VFR through mid-afternoon before lower VFR and MVFR cigs settle in at MSP. Confidence remains high for rain to begin later today and steadier, heavier rain tonight into Thursday morning. Exact timing may vary by an hour or two either way of the 18z MSP TAF given some discrepancies in the guidance. Start time may trend from 22z to 23z-00z for instance. Low confidence on TS/CB through 18z Thursday but opted for a PROB30 for -TSRA/CB after 20z Thursday afternoon. /OUTLOOK FOR KMSP/ FRI...VFR, chc MVFR/-SHRA. Wind NW 10-15 kts. SAT...VFR. Wind NW 10 kts. SUN...VFR. Wind NW 5-10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ DISCUSSION...TDH AVIATION...BPH