textproduct: Great Falls

KEY MESSAGES

- Spring storm will continue to affect much of the CWA today, with periods of rain and well below normal temperatures.

- There will continue to be a chance for showers/thunderstorms most days this week.

DISCUSSION

- Meteorological Overview: Overall, the spring storm continues to affect the CWA this morning. A slow moving upper level low currently over Wyoming is going to move slowly northward through eastern MT over the next few days. This is a bit of a change, which will now result in several days of rainfall over the CWA, with North Central MT likely seeing the heaviest precipitation. It is likely precipitation will now last well into Tuesday over North Central MT with this system. Because of cloud cover/precip, temperatures will not change much from morning lows to afternoon highs, especially over North Central MT.

On Wednesday, the slow moving upper level low should have exited the region, reducing the chances for showers/thunderstorms. However, another upper level low will move from west to east across the CWA on Thursday. The GFS has been showing another band of precipitation to move across the CWA on Thu with this system.

For Friday into next weekend...another slow moving upper level trof is expected to move from west to east across the Pacific Northwest. This will result in an unstable southwest flow aloft over MT, allowing for daily chances of scattered showers/thunderstorms to continue. Afternoon temperatures will begin to warm above seasonal normals by late in the week as well.

- Forecast Confidence & Scenarios: Outside of the convective showers that went through Hill/Blaine counties on Sat evening, the overall rainfall rates with the stratiform precipitation has generally averaged between 0.10 and 0.20 inches of rainfall per hour. Great Falls has had only 1 hour where the precipitation rates were above 0.20 inches so far. The GFS/NAM continue to prog another 1 to 2 inches of rainfall today over North Central MT. Much of North Central MT has now had close to or a bit above an inch of rainfall, thus a 2 day total of 2 to 3 inches of rainfall look on track. An isolated higher 2 day rainfall amount can't be ruled out.

For Southwest MT, expect scattered showers to continue today, but rainfall totals will be much lower over the Southwest, generally between 0.20 and 0.40 inches of rainfall.

Snow levels have been fairly high with this system, generally above 9000 feet, thus any snowfall impacts will be limited to ridge tops. (The freezing level at 6z this morning was near 11,000 feet over Great Falls.)

North winds will gust between 40 and 50 mph today in the Cut Bank and Great Falls area, this will add a bit of chill to the rainfall today.

For Monday, there is a 90 percent of another half inch to an inch of precipitation possible in the Browning/Cut Bank areas. Rainfall amounts will be quite a bit lighter as you go south of this region.

For Thursday, the chance for a quarter of an inch of rain is about 15 percent over North Central MT.

AVIATION

31/12Z TAF Period

Widespread rain will continue through today over North Central MT, with the precipitation more scattered over Southwest MT. Low ceilings and gusty surface winds are expected over North Central MT, with slightly higher ceiling over Southwest MT. Any thunderstorms today will be quite limited, and the probability of adding thunder at a terminal site for today is too low as of now. Brusda

HYDROLOGY

Overall, the probability of widespread flooding over North Central MT continues to decrease. Rainfall rates have been just low enough, that much of the soil has been absorbing the rainfall. Rivers are now just showing signs of responding/increasing with the recent rainfall.

With the bulk of the higher precipitation over with for Southwest MT, no issues are expected over the Southwest.

Over North Central MT, new calculations have reduced the probability of flooding on the Sun River, thus releases have decreased out of Gibson Dam, which also have lowered the chances for flooding along the Sun River.

The probability for flooding on the Dearborn has also decreased.

The two rivers that do remain a bit of a concern are Badger Creek and the St. Mary River. Badger Creek is likely to go into action stage later today, and the St. Mary River is already in action stage. However, impacts along these 2 rivers are very limited and an advisory rather than a warning might be issued later today should the trend continue for these rivers to rise.

The areal flood watch will continue for areas west of I-15 from north of Helena to the US/Canadian border. However, since no flood reports have been received, the probability of areal flooding continues to lower. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 51 41 55 41 / 100 90 70 40 CTB 48 36 47 37 / 100 80 100 80 HLN 54 43 61 42 / 90 80 40 20 BZN 53 37 63 38 / 90 40 20 50 WYS 53 30 63 31 / 80 30 20 20 DLN 57 36 63 38 / 50 30 20 50 HVR 58 39 56 39 / 80 90 90 50 LWT 52 37 57 38 / 90 80 70 40

TFX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Monday afternoon for Cascade County below 5000ft-East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Eastern Pondera and Eastern Teton-Gates of the Mountains-Northern High Plains-Southern High Plains-Southern Rocky Mountain Front.