U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 270600 
Storm Prediction Center ac 270559 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1259 am CDT sun may 27 2018 

Valid 271200z - 281200z 

..there is a slight risk of severe thunderstorms over the High 
Plains region as well as over the Florida Peninsula... 

Severe storms are possible later today into this evening primarily 
from the northern through southern High Plains. A modest threat for 
a few tornadoes will also exist across the Florida Peninsula. 


Cutoff upper low circulation situated over the Great Basin will 
advance very slowly east today with downstream ridge shifting east 
through the plains and MS valley region. At the surface a 
northern-stream low-amplitude shortwave trough moving through 
southern Manitoba will provide the impetus for a cold front to 
continue south into the northern plains and upper MS valley. Farther 
south a dryline will become established over the central through 
southern High Plains. Subtropical storm Alberto is forecast by the 
National Hurricane Center to continue north through the eastern 

..High Plains region and central rockies... 

Post-frontal upslope flow will persist across Wyoming where some low 
clouds may linger into early afternoon. Farther east into the High 
Plains dewpoints generally in the 50s and steep lapse rates will 
support moderate to strong instability as the boundary layer warms 
during the afternoon with MLCAPE from 1500-2500 j/kg likely. Several 
vorticity maxima moving through the upper low circulation will lift 
north through The Rockies and into portions of the High Plains. 
Multiple areas of thunderstorm initiation are likely, including 
within upslope regime over the higher terrain of Wyoming as well as 
farther south along dryline across the central through southern High 
Plains, where the best wind profiles for a few high based supercells 
will exist. Otherwise, multicell storms will be the dominant Mode. 
Storms may remain more discrete with southward extent into the 
plains before weakening during the evening, but some upscale growth 
into lines/clusters may occur from Wyoming into western NE and the 
western Dakotas where storms may persist into the overnight. Large 
hail and damaging wind are expected to be the main threats. 

..FL through southeast Georgia... 

Subtropical storm Alberto is forecast by the NHC to advance north 
and northwest through the eastern Gulf. Satellite imagery shows 
middle to upper-level dry air entraining into the west and southern 
portions of the storm, and this should increase the chance of 
diabatic heating in between the outer convective bands today. A 
broad low-level jet east of the center will augment 0-2 km 
hodographs over the southern two thirds of the Florida Peninsula during 
peak heating, supporting a threat for mini supercells capable of a 
few tornadoes later today. At least a marginal risk for a couple of 
tornadoes will extend farther north into southeast Georgia by late 
afternoon or evening. 

.Dial/marsh.. 05/27/2018 


Mesoscale Discussion

acus11 kwns 270630 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 270629 

Mesoscale discussion 0536 
National Weather Service Storm Prediction Center Norman OK 
0129 am CDT sun may 27 2018 

Areas affected...part of far eastern Montana and southwest ND 

Concerning...Severe Thunderstorm Watch 122... 

Valid 270629z - 270900z 

The severe weather threat for Severe Thunderstorm Watch 122 

Summary...threat for severe wind gusts and hail persists through 
08-09z across far eastern Montana and across west-central into 
southwest North Dakota. Ww 122 may need to be extended in time 
beyond its current 07z expiration. 

Discussion...at 06z, mosaic radar imagery showed a band of storms, 
with a history of producing severe wind gusts of 56 kt and 57 kt, 
extended from western McKenzie County, ND to Dawson County, Montana. 
Additional storms were forming along the leading edge of the primary 
band in southern Dawson County within a regime of low-level warm 
advection. Objective analysis at 05z indicated a minimum in 
mixed-layer inhibition and residual north-south corridor of 
surface-3-km lapse rates of 6 c/km astride of the Montana/ND border. 
These thermodynamics likely allowed stronger winds (57 kt) to reach 
the surface as reported at ksdy at 0456z, and may continue to 
support a severe-weather threat in the short term into far western 
ND. Current movement of the band of storms is at 20-25 kt. 
Although this slow forward speed should limit a severe gust threat, 
apparent cold-pool development could result in some potential 
increase in forward motion. However, stronger surface-based 
inhibition with eastward extent across western ND suggests an 
eventual reduction in threat for storms producing severe wind gusts. 

Effective bulk shear remains strong and combined with moderate 
elevated instability should allow for a few storms to become capable 
of producing hail locally exceeding severe caliber into the 

.Peters.. 05/27/2018 

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


Latitude...Lon 46740553 47960349 48120287 47440165 47000107 46650092 
46010113 45940200 45920319 45920395 46130481 46740553