684 FXUS65 KTFX 311009 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 359 AM MDT Fri May 31 2013 .DISCUSSION... Today through Sunday...Rain will continue again today across north-central Montana with lesser chances over southwest Montana as a persistent upper-level low pressure system gradually moves further east into the Dakotas. Rain will be moderate at times over eastern portions of the forecast area, especially across Hill, Blaine and Fergus counties with light to moderate elsewhere. Additional rainfall amounts of 0.25 inches to 1.25 inches are likely through this evening with isolated higher amounts in the mountains where over 3.00 inches of moisture has fallen in the last 24 hours. Will continue the Areal Flood Watch as well as a Small Stream Advisory for southeastern Hill County and Small Stream Flood Warning for parts of Fergus County where several streams/creeks are out of their banks and impacting roadways. Remember not to cross any flooded roadways. Rain will taper to showers this afternoon and then off by midnight. Models hint at some clearing possible across much of the area later tonight and given the abundant low-level moisture across north-central Montana, have added the potential for patchy fog after midnight into early Saturday morning. Weak upper-level ridging will give way to drier conditions on Saturday with temperatures rising to around seasonal averages. The break will be temporary as another storm system pushes into the Pacific Northwest Saturday night. This Pacific system will bring additional moisture as well as a surface cold front across north-central and southwest Montana on Sunday and have increased pops as a results. There are some minor differences in timing between the models, but with warming temperatures Sunday afternoon and an evening frontal passage, there should be enough instability for isolated to scattered thunderstorms. If the progression of this system slows, then the precip chances will decrease. MLV Sunday night through Friday...Medium range models are in good agreement that another upper level low will move over the northern Rocky Mountains Sunday night through Monday. Widespread rain and high mountain snows can be expected for this period with scattered showers lingering across the forecast area through Tuesday. The upper low moves slowly east on Wednesday allowing a weak shortwave ridge to develop over Montana for more seasonable temperatures. Model solutions diverge significantly for Thursday and Friday as the GFS stalls the upper low over the Great Lakes region but the ECMWF continues to progress the low eastward. Over the Rockies this difference results in the GFS continuing to build the upper ridge for generally warm and dry weather. However, the ECMWF drops a shortwave trough from the Gulf of Alaska over Montana for another round of showers and cooler temperatures. Have trended the forecast for Thursday and Friday toward climatology with low forecast confidence for now and will see how model trends go in the coming days. mpj && .AVIATION... Updated 0416Z. A broad upper level low pressure trof will keep the airmass cool and moist. Widespread rain and MVFR/IFR CIGS/VSBYS are expected across north central Montana, including KHVR, KLWT, KCTB, and KGTF. Southwest Montana, KHLN and KBZN, will generally remain VFR although showers and local MVFR CIGS are possible. Mountain obscuration across the region is expected. && .HYDROLOGY... Widespread light to moderate rainfall will continue across the area through today. The highest potential additional rainfall is expected along and east of line from Toole County southeast through Chouteau County into Judith Basin County. Therefore, will continue the areal Flood Watch for this area through early this evening, as river rises and minor creek/stream flooding remain possible. In fact, there has been a report that water was flowing over a rural road between Beaver Creek Reservoir and Bear Paw Lake in Hill County. Therefore, a Flood Advisory for small streams has been issued for southeastern Hill County, which is in effect through Friday afternoon. The situation will continue to be monitored for possible further HYDROLOGIC highlights if conditions warrant. Coulston/MLV && .PRELIMINARY POINT TEMPS/POPS... GTF 55 39 67 44 / 100 40 10 10 CTB 56 38 68 43 / 90 20 10 20 HLN 59 40 69 45 / 40 20 10 10 BZN 58 36 68 40 / 40 30 10 10 WEY 55 31 63 35 / 30 20 10 10 DLN 60 35 69 41 / 20 20 10 10 HVR 60 42 69 44 / 100 40 10 10 LWT 49 37 63 41 / 100 60 10 10 && .TFX WATCHES/WARNINGS/ADVISORIES... FLOOD WARNING for small streams in Fergus County until 445 pm Friday. FLOOD WATCH through Friday afternoon Blaine...Chouteau... Fergus...Hill...Judith Basin...Liberty...Toole. FLOOD ADVISORY for small streams through 315 pm MDT Friday for southeastern Hill County. && $$ weather.gov/greatfalls