681 FXUS65 KTFX 221137 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 530 AM MDT Thu Aug 22 2013 AVIATION SECTION UPDATED .DISCUSSION... Thursday through Saturday...A few shortwave impulses will continue to move across the area as a large scale ridge of high pressure aloft dominates the weather pattern. Winds today will transition to a more southwesterly origin...allowing any showers and thunderstorms that develop to move off to the northeast. The shortwaves that are expected to move through the area today and Friday will allow for an increase in shower activity mainly over the higher terrain and with the peak of the activity still expected in the late afternoon and early evening hours. Maximum temperatures will warm back up to around 10 degrees above seasonal averages through the short term. Moisture aloft will continue to move into the area providing decent potential for showers and thunderstorms especially on Thursday. With the warm dry temperatures near surface any showers or thunderstorms that develop will have the potential to create strong gusty winds in their vicinity. Suk Saturday Night through Thursday...Strong high pressure ridge parked over the central US is forecast to persist well into next week. Located in the transition zone between the western flank of the ridge and the stationary longwave trof across the eastern Pacific Ocean, Montana will remain under southwest flow aloft which will keep temperatures 5-10 degrees above normal with daily highs in the mid 80s to low 90s over the plains and valleys. The only noteworthy disagreement in the forecast models is in their expectations for precipitation through the extended period. Overall, the GFS model is a bit wetter than the ECMWF model as it is favors wider coverage of monsoonal moisture coming up the ridge's west side from Mon-Wed. This is a slight change from GFS runs of the past few days, which trended toward drier conditions by keeping the monsoonal moisture confined to far southwest MT and Wyoming, which interestingly, is the current ECMWF solution. Current forecast grids lean toward lower chances of precipitation, with 20-30% chances along the Rocky Mtn Front and over the southwest mountains from Sun to Wed and over the Hiline counties on Sun evening. Other than a stray thunderstorm or two on Sun and Tues evenings, the remainder of central and north central MT looks to be quite dry, with most locations likely not receiving any rainfall at all. Waranauskas && .AVIATION... UPDATED 1130Z. Southwest flow aloft around a strong high pressure ridge centered over the Midwest states will keep VFR conditions over central and southwest MT today. Combination of Pacific and monsoonal moisture will gradually move up the west side of the ridge, bringing increasing mid- and high-level clouds from 18Z onward. Pockets of higher instability over southwest MT will combine with the moisture to produce isolated thunderstorms along/south of a KHLN-to-KLWT line this aftn/early eve, with convective activity dissipating by 02-03Z. Surface winds generally 6-10 kts today, but could see some brief gusty outflow winds (30-35 kts) near any thunderstorms. Waranauskas && .FIRE WEATHER... UPDATED 2055Z. With increasing thunderstorm activity, continued dry conditions, and ongoing fires across southwest/western Montana Thursday into Friday, NWS Missoula has issued Fire Weather Watches and Warnings for these areas. The storms will initially move into southwest Montana on Thursday, so the warning will include Fire Weather Zones 110/111 (which include portions of Beaverhead/Madison/Jefferson Counties) for Thursday afternoon through Friday evening. The storms will then spread north, resulting in Watches including Fire Zones 105/108 (which include western portions of Lewis and Clark County, as well as western portions of the Rocky Mountain Front). Thunderstorm activity will also increase into North Central Montana on Friday. However, there seems to be more moisture (precipitable water values in excess of 1 inch) available for these storms than those to the west and south. This may result in more of a mix of wet and dry thunderstorms. Regardless, conditions near the surface will be dry enough to support gusty erratic winds with the expected lightning strikes. This may cause additional fire starts, but the threat for rapid fire spread is less certain. Will therefore include a headline in the Fire Weather Forecast for now and discuss the situation with fire officials for possible Watches into north central Montana. Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 91 58 88 54 / 10 20 40 30 CTB 89 54 85 52 / 0 10 30 30 HLN 90 59 88 57 / 20 30 40 30 BZN 89 52 87 50 / 30 30 40 30 WEY 80 42 77 40 / 30 30 30 20 DLN 86 52 83 49 / 30 40 40 30 HVR 89 59 91 57 / 0 10 30 40 LWT 86 57 88 54 / 10 20 40 40 && .TFX WATCHES/WARNINGS/ADVISORIES... FIRE WEATHER WATCH from late tonight through Friday afternoon Central and Southern Lewis and Clark...Northern Rocky Mountain Front...Southern Rocky Mountain Front. FIRE WEATHER WARNING from Noon MDT today through Friday evening Beaverhead...Jefferson...Madison. && $$ SHORT TERM...Suk LONG TERM...WARANAUSKAS AVIATION...WARANAUSKAS weather.gov/greatfalls