U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 030058 
Storm Prediction Center ac 030056 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0756 PM CDT Wednesday Sep 02 2015 

Valid 030100z - 031200z 

..no severe thunderstorm areas forecast... 

isolated to scattered thunderstorms should persist for a few more 
hours from the upper Great Lakes southeastward to the Virginia/North 
Carolina Tidewater region...and also...over parts of Arizona and the 
southern rockies. Isolated thunderstorms are possible through late 
tonight. Severe-wind potential looks too isolated and poorly 
focused for any risk areas. 

Large-scale upper-air pattern will remain dominated by troughing 
over Pacific coast region...extending southward from cyclone over British Columbia...and 
downstream rigs from Southern Plains north-northeastward across Hudson Bay. Downstream 
from that ridge...these shortwave troughs were noted in 
moisture-channel imagery... 
1. Over WI...western lower Michigan and western ls...and forecast to move slowly 
east-southeastward across Upper Michigan and northern lm through remainder period. 
2. Over Virginia...forecast to weaken considerably and move southeastward off Atlantic 
coast near Hampton Roads overnight. 
3. Persistent...elongated...quasistationary cyclonic-shear zone 
from Bay of Campeche northward across western Gulf then northeastward over middle south to 
lower Ohio Valley. Several embedded/mesoscale vortices were 
apparent...though overall synoptic feature should remain near 
present location/orientation through 12z. 

At surface...nebulous pattern was apparent at 00z over most of 
Continental U.S....dominated by mesoscale features such as weak lows...troughs 
and outflow boundaries. Exceptions included quasistationary frontal 
zone from central lower Michigan westward through weak low over southern WI/Minnesota 
border area...then nwwd across northwestern Minnesota. Wavy dryline was evident 
from southern sk across western Dakotas...western sandhills of Nebraska...western Kansas...and 
north-S segment of Texas/nm border...southward across Texas Big Bend region. 

..upper Great Lakes to NC/Virginia Tidewater... 
Isolated to locally scattered/clustered thunderstorms persist across broad 
swath from northern WI and portions Upper Michigan...lower Michigan...le...and 
Ohio...to northestern NC. Activity should continue moving generally southeasterly 
through evening with slow weakening of both coverage and intensity 
expected overall. An isolated damaging thunderstorm gust with winds approaching 
severe limits cannot be ruled out anywhere from WI and lower Michigan to northestern 
NC...within broad plume of rich low-level moisture that can support 
substantial water loading in downdrafts. However...with gradual 
diabatic surface cooling and growing coverage of outflows each acting to 
stabilize boundary-layer air mass across this swath...severe 
potential appears to have become too isolated and unfocused to 
warrant continuation of at or above 5%/marginal categorical designations. 

... Rockies... 
widely scattered to scattered thunderstorms were evident over roughly eastern 
1/2 of Arizona...much of nm except southeastern plains...and portions western/southern Colorado. 
Most of this activity has been diurnally driven with heating of 
higher terrain...amidst favorable low-level moisture and minimal 
late-afternoon mlcinh. Available/observed radiosonde observations over this region depict 
favorably deep/well-mixed boundary layers to support isolated strong 
gusts...but also...enough boundary-layer dryness that only a few degree 
f surface cooling is needed in most instances to eradicate most MLCAPE 
present. While a damaging gust cannot be ruled out...risk is too 
isolated/unfocused to place any definitive categorical areas. 

.Edwards.. 09/03/2015 

Mesoscale Discussion

acus11 kwns 021935 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 021935 

Mesoscale discussion 1757 
National Weather Service Storm Prediction Center Norman OK 
0235 PM CDT Wednesday Sep 02 2015 

Areas affected...eastern WV...Maryland Panhandle...cntrl/ern Virginia 

Concerning...severe potential...watch unlikely 

Valid 021935z - 022100z 

Probability of watch issuance...5 percent 

Summary...scattered thunderstorms are expected to persist through the 
afternoon with the low potential for some damaging wind gusts and 
hail. Minimal severe coverage and a generally marginal threat will 
preclude the need for a ww. 

Discussion...regional radar imagery shows gradually increasing thunderstorm 
coverage ahead of a weak upper low currently moving across central WV 
and into northern Virginia. Middle-level lapses rates are poor -- less than 6 degree 
c per km based on the recent mesoanalysis -- but warm surface 
conditions and good low level moisture /upper 60s dewpoints/ are 
contributing to airmass destabilization. Latest mesoanalysis 
estimates MLCAPE over 1000 j/kg for much of the region. A very 
modest increase in middle-level winds is possible as the low moves 
through but even with this increase shear is expected to remain weak 
across the area. This lack of shear will preclude storm organization 
and temper the overall severe threat. Precipitation loading within 
the stronger updrafts resulting from storm mergers and/or quick 
development on outflow boundaries may result some localized damaging 
winds with some hail also possible with the strongest updrafts. 

.Mosier/Thompson.. 09/02/2015 

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


Latitude...Lon 37887996 38518005 39127981 39457941 39647919 39717888 
39727793 39697775 39477730 39357718 38297645 37747630 
37217656 36887697 36657745 36697826 36847902 37487970