textproduct: Billings

KEY MESSAGES

- A few strong thunderstorms are possible over southeast Montana today. - Flood Watch in effect through Sunday for much of the area. Widespread precipitation through the weekend, with potential for locally heavy rainfall through tonight. - Widespread 50-95% chance of an inch of rainfall. 50-80% chance of two inches of rainfall for portions of south central Montana.

UPDATE

Upper low continues to evolve very slowly over southern ID, leaving our forecast area under a very diffluent region aloft. Easterly 700mb winds have veered to southerly over the south, but remain easterly over the north...and as a result the heaviest precip as of 1030z is across our north. This includes Hysham to Miles City where t-storms recently developed along what amounts to an elevated warm front (w/ instability). As the low continues to move slowly eastward into western WY today, precip w/ the trowal should wrap back southward, with upslope enhancement from Red Lodge to Sheridan tonight & Sunday. Our southern upslope areas seem to be where the forecast is most uncertain at this point, as they depend on mid level flow turning to the N-NE. Otherwise, showers and some embedded t-storms continue. If there is a risk of a few strong storms today it will be in our S/SE from Sheridan across far southeast MT, where instability will be greatest, but HREF continues to show helicity tracks most favored further south in eastern WY. Something to watch.

Billings airport is up to 2.03" of total rainfall since Friday evening. This already ranks as the 3rd wettest 2-day precip total in September (dating back to 1934). Another 0.18", which is all but certain, will put the current event in the top spot for 2-day precip at Billings in September.

JKL

AVIATION

10z discussion.

A slow-moving weather system will bring widespread rain showers and some embedded thunderstorms today and tonight, with patchy nighttime fog as well. MVFR/IFR flying conditions will be common, and all TAF sites will be impacted by this system. Mountains will be mostly obscured through the period. JKL

PRELIMINARY POINT TEMP/POPS

Tdy Sun Mon Tue Wed Thu Fri ------------------------------------------------------- BIL 059 051/063 049/072 050/077 052/079 053/081 053/080 +/T 98/W 20/B 00/U 00/B 10/U 00/B LVM 059 043/066 041/075 044/078 046/079 047/081 048/080 +/T 84/W 00/U 00/U 01/U 00/U 00/B HDN 063 048/063 046/073 045/079 049/081 048/083 049/083 +/T 97/W 30/B 00/U 11/U 00/U 00/U MLS 065 052/062 049/070 050/078 053/080 053/082 055/083 +/T 99/W 31/B 00/U 12/W 10/U 00/U 4BQ 066 052/061 049/068 049/077 053/079 053/082 055/082 +/T 99/T 61/B 00/U 12/T 10/U 00/B BHK 065 047/060 044/067 045/075 049/080 050/083 051/082 7/T 99/W 41/B 00/U 01/U 10/U 00/B SHR 063 044/063 042/071 042/077 046/079 046/082 047/083 9/T 98/T 41/B 00/U 11/U 10/U 00/U

BYZ WATCHES/WARNINGS/ADVISORIES

MT...Flood Watch in effect through Sunday afternoon FOR ZONES 29>34-36-37-40-42-56>58-63>68-138-139-141-169>173-228-235. WY...Flood Watch in effect through Sunday afternoon FOR ZONES 198-199.