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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Wednesday
• 
• High: 86 °
• Low: 54 °
• T-Storms

• Thursday
• 
• High: 72 °
• Low: 48 °
• Chance of a Thunderstorm

• Friday
• 
• High: 68 °
• Low: 50 °
• Chance of T-Storms

• Saturday
• 
• High: 68 °
• Low: 50 °
• Chance of Rain

• Sunday
• 
• High: 72 °
• Low: 52 °
• Chance of Rain

Area forecast discussion 
National Weather Service Great Falls Montana 
1155 am MDT Wed Jun 19 2013 


..update to aviation... 


..Strong to possibly severe thunderstorms this afternoon into 
this evening... 


Update... 


Satellite imagery this morning shows a fairly vigorous upper level 
low centered over eastern or, poised to track east into the 
northern rockies tonight. As the upper low tracks east today, flow 
aloft will increase from the south and southeast with surface low 
development occurring over central Montana late this afternoon and 
evening. Southeast flow in the low levels will hold relatively high 
dewpoint airmass at the surface over north central Montana which will 
lead to moderate instability late this afternoon and evening. Only 
question remaining with respect to thunderstorm strength is the 
impact of cloud cloud-cover currently over the central and western 
Montana. Latest satellite trends do show some of this cloud field 
beginning to break up with with lesser cloud-cover upstream in S to 
southeast flow aloft which should allow for the necessary surface heating 
for moderate instability to be realized. Expect initial storms to 
develop after noon over the higher terrain of western and SW Montana 
with these storms moving north and intensifying/organizing late 
this afternoon and evening as they encounter Richer low level 
moisture and more favorable shear. Large hail and damaging winds 
still appear to be the main threat with storms this 
afternoon/evening and cannot rule out a small (5%) threat for 
tornadoes as weak low level helicity values look to briefly reach 
marginal levels across portions of north central Montana. Current 
gridded forecast covers the situation well with only minor updates 
required this morning. Hoenisch 


&& 


Aviation... 
updated 1755z. 
There strong possibility for severe thunderstorms with hail in 
excess of one inch in diameter and wind gusts in excess of 50 knots 
over central and north central Montana...especially in the vicinity 
of khvr...lwt...and to a lesser degree kgtf. Also some of the 
thunderstorms will have brief heavy rain with IFR ceilings and 
visibilities. Expect thunderstorms to develop over southwest Montana 
by mid-afternoon then intensify as they move over the plains. Suk 


&& 


Hydrology... 
showers and thunderstorms are expected to develop once again this 
afternoon over the Rocky Mountain front and the adjacent plains 
along a surface cold front. These showers and thunderstorms are 
then expected to spread east across the plains of north central 
and central Montana later this afternoon and continue into this 
evening. Forecast models are predicting significant rainfall with 
these showers, which is expected to occur in rapid bursts with the 
thunderstorms. Some localized flash flooding occurred with storms 
along the Rocky Mountain front Tuesday evening. However, the 
greater area of concern is across eastern portions of north 
central and central Montana that still have moist soil that would 
not be able to absorb much rapid rainfall. Forecast models also 
indicate that this area will receive the greatest amount of 
rainfall. Taking these factors into consideration, have decided to 
issue a Flash Flood Watch from noon MDT today until midnight MDT 
tonight for all of north central and central Montana. The greatest 
threat for flash flooding for the Rocky Mountain front and 
adjacent plains will be this afternoon, while the greatest threat 
in the east will likely be after 5 PM MDT. 


&& 


Previous discussion... 
/issued 555 am MDT Wed Jun 19 2013/ 


Today through Friday...thunderstorms from overnight have exited 
the area, but another round of potentially severe weather is on 
tap for today. The Pacific low pressure system that brought 
thunderstorms to the western portion of the forecast area 
yesterday will slowly move into the Pacific northwest today. The 
moist, unstable, and diffluent southerly flow ahead of the system 
will combine with a strong embedded disturbance and the associated 
cold front over the area for more widespread thunderstorm 
development than yesterday. Therefore, the Storm Prediction Center 
has all of north central/central Montana under a slight risk for 
severe thunderstorms today. While some storms over the Western 
Plains of north central/central Montana may see marginally severe 
thunderstorms (wind gusts around 60 mph, hail around 1 inch in 
diameter), the greater focus will be on the eastern plains. 
Surface winds there will be breezy and out of the east ahead of 
the cold front, which will advect moist air (dewpoints in the 
upper 50s to lower 60s) into the area and enhance the instability. 
The surface winds will also combine with the stronger winds aloft 
to provide strong wind shear (with regard to both speed and 
direction) to that area as well. The enhanced instability and 
shear will focus the potential for significantly strong 
thunderstorms (hail possibly 2+ inches in diameter, wind gusts in 
excess of 70 mph) on the eastern tfx plains. Wind shear may even 
be strong enough to possibly generate an isolated tornado. 
However, all of these ingredients seem to come together later this 
afternoon, which means that thunderstorm development there may not 
occur until after 4 or 5 PM MDT, while storms farther west will 
develop after 1 PM MDT. Forecast models are also indicating that 
these storms may produce heavy rainfall, so have issued a Flash 
Flood Watch for the area as well (please see hydrology section for 
details). While storms will generate over the higher terrain of 
southwest Montana, the potential for severe storms there is low. 
Overall, storms will exit the area to the east with the passage of 
the cold front this evening. Westerly downslope winds will help 
limit overnight precipitation to the western mountains. A much 
cooler airmass will also move into the area, possibly bringing 
light measurable snow to the mountain peaks. Winds will likely 
approach high wind criteria along the Rocky Mountain front on 
Thursday, but am not anticipating a need for high wind highlights 
at this time. The Pacific low pressure system will linger through 
the day on Friday, keeping a chance of showers and (likely weak) 
afternoon/evening thunderstorms over the area, as temperatures 
remain about 10 degrees cooler than normal. Coulston 


Friday night through Wednesday...an upper low over the Pacific 
northwest early Friday evening is forecast to weaken as it moves 
over the forecast area on Saturday. Models are fairly wet over 
southwest and north central Montana on Saturday so have increased 
the chances of precipitation especially over north central 
Montana. The remnants of the upper low move out by late Saturday 
night and by early Sunday morning it appears the only threat for 
precipitation will be over north central Montana and possibly the 
mountains of the Rocky Mountain front. On Sunday an upper ridge 
will move through the forecast area and expect a mostly dry 
period but then southwest flow aloft returns next week. Models 
differ on shortwave details and associated precipitation 
patterns. Due to these inconsistencies will go with generally a 
chance of showers/thunderstorms over the mountains of the Rocky 
Mountain front with a slight chance of showers/thunderstorms 
elsewhere. Cool air associated with the upper low will result in 
highs on Saturday of only 55 to 65 except over north central 
Montana where highs will be closer to 70. Thereafter expect 
gradually warming temperatures. Blank 


&& 


Preliminary point temps/pops... 
gtf 76 47 67 43 / 80 40 20 20 
ctb 74 45 63 41 / 90 70 20 20 
hln 75 46 65 43 / 70 40 30 20 
bzn 81 42 68 39 / 40 30 30 20 
wey 69 32 60 31 / 30 30 20 10 
dln 72 39 62 37 / 50 50 30 20 
hvr 88 52 72 47 / 60 100 20 20 
lwt 83 45 68 42 / 50 80 20 30 


&& 


Tfx watches/warnings/advisories... 
Flash Flood Watch through this evening Blaine...Cascade... 
Chouteau...eastern Glacier...eastern Pondera...eastern Teton... 
Fergus...hill...Judith Basin...Liberty...northern Rocky Mountain 
front...southern Rocky Mountain front...Toole. 


&& 


$$ 


Weather.Gov/greatfalls