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Area forecast discussion 
National Weather Service Great Falls Montana 
1040 PM MDT Tuesday Aug 19 2008 


Aviation discussion updated... 


Update... 
widespread severe thunderstorms have come to an end...with a summary 
storm report sent out. 


However...a band of light rain showers has developed from Lincoln 
northeastward to Havre...thus probability of precipitation have been raised in this 
region...but total precipitation amounts will generally be less than a 
tenth of an inch. Humidities have increased and the threat for dry 
thunderstorms has diminished...so the red flag warning has been 
cancelled. Overnight lows have been raised in a few locations...as 
cloud cover will keep temperatures on the mild side. 


Looking ahead...expect another round of showers and thunderstorms on 
Wednesday afternoon/evening...but the precipitation activity should not be 
as widespread as todays activity. The main cool front will arrive on 
Thursday...with a seasonable day expected on Friday. A return to 
Summer like temperatures and dry conditions is expected on 
Saturday...with the nice weather continuing through Sunday. Brusda 


&& 


Aviation... 
surface cold front has moved into eastern Montana but residual instability 
and moisture associated with upper level trough axis lifting northeastward 
across western Montana is continuing to produce light rainshowers and a few 
thunderstorms along and east of a kctb-to-k3du line. O6z tafs 
extended duration of precipitation until 08-09z. Clouds will become 
mostly scattered by sunrise...but coverage increases back to broken by early 
afternoon Wednesday as next upper trough arrives from the west. Scattered showers 
and thunderstorms expected to develop mainly north of a khln-to-klwt 
line during the afternoon/evening and then residual showers after sunset. 
Less chance of severe storms tomorrow but some cells may be 
strong...with variable and gusty outflow winds. Conditions will 
remain VFR this evening and tomorrow except for brief periods of MVFR 
near thunderstorms. Waranauskas 


&& 


Previous discussion... 
/issued 710 PM MDT Tuesday Aug 19 2008/ 
tonight through Thursday...strong upper low in the Gulf of Alaska 
will move southeast and weaken as it moves into the Pacific 
northwest on Thursday. Expect increasing southwest flow aloft over 
the area along with an increase in moisture. For tonight a shortwave 
will move northeast through the area this evening. A line of strong 
thunderstorms will move out ahead of this shortwave the rest of this 
afternoon and early evening. Expect local severe weather with the 
storms. For late tonight into early Thursday expect a series of weak 
shortwaves to affect the area and there will likely be some weak 
instability. Will continue with the slight chance to chance probability of precipitation. On 
Thursday there is the potential for better lift as a strong jet 
streak moves into central Montana. There is some question about how 
much moisture will be available. Inherited forecast which increases 
the chances of precipitation from Wednesday to Thursday looks good. 
Blank 


Thursday night through Sunday night...models are in decent 
agreement for Thursday night moving the axis of the upper trough 
from western Montana to the Dakotas border by morning. Scattered 
showers and thunderstorms will taper off from west to east 
overnight with snow levels expected to drop to between 6500 and 
7000 feet. Northwest flow aloft sets up over my forecast area on 
Friday as the trough moves into the upper Midwest...with isolated 
instability showers lingering over the area. Weak upper level 
ridging builds over the northern Rocky Mountains Friday night 
through Sunday for clearing skies and dry conditions...with 
temperatures warming back above seasonal averages during the 
weekend. Mpj 


Monday and Tuesday...latest extended models depict a cold front 
moving in during this period. Used climatology for precipitation 
chances. Temperatures are expected to be near normal as the front 
move through the region. Saucier 


&& 


Preliminary point temps/pops... 
gtf 59 84 60 76 / 60 20 20 50 
ctb 57 73 52 72 / 30 20 40 40 
hln 61 84 58 78 / 40 20 30 50 
bzn 57 88 54 83 / 20 20 20 40 
wey 49 75 48 74 / 20 20 20 40 
dln 53 78 51 75 / 20 20 20 40 
hvr 61 88 56 81 / 40 20 20 40 
lwt 56 86 53 76 / 20 10 20 50 


&& 


Tfx watches/warnings/advisories... 


None. 
&& 


$$ 


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