U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 240554 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1254 am CDT Thursday Jul 24 2014 


Valid 241200z - 251200z 


..there is a slight risk of severe thunderstorms this afternoon into tonight across 
parts of eastern Montana into western and central North 
Dakota...perhaps parts of adjacent northern South Dakota... 


... 
A few severe thunderstorms capable of producing large hail and 
strong wind gusts are possible across parts of eastern Montana into 
western and central North Dakota this afternoon into tonight. 
Strong storms...with potential for localized damaging wind 
gusts...may also develop across parts of the central and southern 
Appalachians into the southern middle Atlantic coast states today. 


... 
The significant short wave trough and embedded closed low now over 
the Pacific northwest appear likely to continue slowly inland during 
this forecast period...as an upstream impulse progresses across the 
northeast Pacific...toward the British Columbia coast. With 
subtropical ridging currently prominent across much of the 
intermountain west/rockies and plains...the lead system is forecast 
to turn northeastward around its crest...across the Canadian and 
northern U.S. Rockies...into Alberta and Saskatchewan. Models 
suggest that substantive middle-level height falls will generally be 
confined to Montana and portions of the Dakotas...with only minor 
weakening of the subtropical high...although its center may shift 
southeast of the central rockies into the southern High Plains. 


Otherwise...little change to the large-scale upper pattern is 
expected...with amplified troughing persisting east of the 
Mississippi Valley through the Atlantic Seaboard. The leading edge 
of low-level cooling/drying associated with this feature is expected 
to advance southeast of the Ohio Valley into the South Atlantic and 
Gulf Coast states. At the same time...a southerly return flow will 
contribute moistening across the central into northern 
plains...ahead of the northwestern upper troughing. However...this 
is generally expected to occur beneath very warm and capping 
elevated mixed layer air advecting northeast and east of the 
northern and central rockies. 


Highest probabilities for thunderstorms during this period appear to 
exist ahead of the front...across the southeastern u... well as 
within a plume of monsoonal moisture from the southern plateau 
through the central rockies. But at least scattered thunderstorm 
activity is expected within a Lower/Middle tropospheric warm advection 
regime developing northeast of the middle Missouri Valley...as well as 
ahead of a cold front advancing into the western Dakotas by late 
tonight. 


..northern and Central Plains... 
Stronger middle-level height falls are not expected to reach eastern 
Montana and the western Dakotas until at least late this 
afternoon...perhaps this evening. And very warm elevated mixed 
layer air probably will suppress vigorous convective development 
within the corridor of higher boundary layer moisture content along 
the pre-frontal surface trough across the region. However...the 
very steep middle-level lapse rates associated with this air mass will 
contribute to sizable cape...and a rather broad area with at least a 
conditional risk for severe storms. 


It currently appears that...through much of the afternoon 
hours...any thunderstorm activity will be widely scattered in 
nature. Activity probably will form across the higher terrain 
near/west of the north Central High plains...in response to daytime 
heating and orographic forcing. But isolated/widely scattered storm 
development may not be out of the question within a zone of enhanced 
Lower/Middle tropospheric warm advection...near a southerly 850 mb 
jet...on the eastern edge of the elevated mixed layer air across the 
eastern Dakotas into Minnesota/Iowa. 


Otherwise...it appears possible that forcing along/ahead of an 
eastward advancing cold front could support storm initiation across 
parts of eastern Montana as early as 21-23z. Although the stronger 
middle/upper flow associated with the approaching upper trough may lag 
to the west of the front...pre-frontal vertical shear across eastern 
Montana into North Dakota still appears sufficient for organized 
convective development...including supercells...given expected mixed 
layer cape of 2000-3000+ j/kg. 
The evolution of a mesoscale convective system capable of producing 
one or two swaths of potentially damaging wind gusts seems at least 
a possibility as upper forcing spreads eastward into the northern 
plains this evening. 


..cntrl/southern Appalachians into southern middle Atlantic coast region... 
Weak Lower/Middle tropospheric lapse rates probably will limit cape 
along/ahead of the southward advancing frontal zone today. 
However...in the presence of seasonably high moisture 
content...modest westerly middle-level flow may enhance convective 
development...supporting at least low probabilities for storms 
capable of producing potentially damaging wind gusts. 


.Kerr/dial.. 07/24/2014 






Mesoscale Discussion


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Storm Prediction Center mesoscale discussion 240741 
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Mesoscale discussion 1455 
National Weather Service Storm Prediction Center Norman OK 
0241 am CDT Thursday Jul 24 2014 


Areas affected...parts of eastern Montana into northwestern ND 


Concerning...Severe Thunderstorm Watch 437... 


Valid 240741z - 240945z 


The severe weather threat for Severe Thunderstorm Watch 437 
continues. 


Summary...a band of storms -- including embedded strong/severe cells 
-- continues moving east-northeastward across northestern Montana...within ww 437. Isolated 
severe risk may spread eastward into northwestern ND over the next few 
hours...where need for a new ww remains uncertain. 


Discussion...latest radar imagery shows a band of strong/locally 
severe storms moving across Phillips/Garfield counties and into 
Valley County Montana at this time...with the strongest storms now on the southern 
edge of the band /over Garfield County/. Damaging winds and large 
hail remain possible with these storms -- particularly the 
newly-evolving Garfield County cells. 


The storms -- slightly elevated at this time above a stabilizing boundary 
layer -- are moving through the axis of greatest mixed-layer cape 
at this time /per objective analyses/. That said...ample elevated cape 
still resides downstream into ND. Given ongoing warm advection 
associated with a southerly low-level jet supporting background ascent 
across this area...isolated severe storms /capable of producing 
large hail/ may indeed survive/spread across northwestern ND in the next 
several hours -- which could require downstream ww consideration. 


.Goss/corfidi.. 07/24/2014 


..please see www.Spc.NOAA.Gov for graphic product... 


Attention...WFO...bis...ggw...tfx... 


Latitude...Lon 46880737 49000867 49040412 48910212 48370060 47960048 
47550090 47550209 47370484 46900580 46880737