SPC - No watches are valid as of Wed Feb 21 07:50:01 UTC 2018

No watches are valid as of Wed Feb 21 07:50:01 UTC 2018.


SPC MD 78

MD 0078 CONCERNING WINTER MIXED PRECIPITATION FOR PORTIONS OF NORTHERN AND CENTRAL IL INTO CENTRAL MO
MD 0078 Image


Mesoscale Discussion 0078
NWS Storm Prediction Center Norman OK
0918 PM CST Tue Feb 20 2018

Areas affected...portions of northern and central IL into central MO

Concerning...Winter mixed precipitation 

Valid 210318Z - 210915Z

SUMMARY...Rain will transition to a wintry mix of freezing rain,
sleet and snow across parts of northern and central IL into central
MO over the next several hours. This wintry mix is expected to
continue through the overnight hours, though precipitation rate
should remain light.

DISCUSSION...A slow, eastward-advancing cold front was draped from
roughly northwestern IN into northwest AR this evening. Cooler
temperatures are filtering southward across the mid-MS Valley, with
readings generally in the 32-37 degree F range from near Chicago
toward St. Louis and Springfield MO. Light to moderate precipitation
was occurring over this area with mainly rain noted on the eastern
edge of the MCD area with a mix of precip types further west. This
transition from rain to a wintry mix will slowly progress eastward
through 09z. Precipitation should generally remain light as heavier
precipitation translates eastward with the front. Freezing rain
rates up to 0.05 inches per 3 hours are expected through the night.
Sleet and occasionally light snow may mix with freezing rain.

..Leitman.. 02/21/2018

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...LOT...ILX...LSX...DVN...SGF...

LAT...LON   41808743 40958789 40198839 39228910 38389018 37909104
            37389207 37279259 37309306 37609318 37959312 38549267
            39049218 40099101 40859017 41418940 41998851 42128797
            42038771 41808743 

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SPC Feb 21, 2018 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1144 PM CST Tue Feb 20 2018

Valid 211200Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN
TEXAS TO WESTERN MISSISSIPPI...

...SUMMARY...
Thunderstorms are forecast from Texas to the Ohio Valley and
Appalachians today into tonight, and a few of these storms may be
strong to severe from the Sabine Valley to western Mississippi.
Locally damaging winds and perhaps a tornado will be the main
threats.

...Synopsis...
The mid/upper pattern across the country will witness little
large-scale change today. An impressive ridge will persist
along/offshore the East Coast, while a western-US trough is
reinforced by a jet maximum advancing southward along the California
coast. Between the two, a broad corridor of strong southwesterly
flow will persist from the southern Plains to the Great Lakes
region. Meanwhile, surface high pressure will build over the
northern Plains and upper Midwest, helping push a cold front
southeast across southern/eastern Texas, the lower Mississippi
Valley, and the Ohio Valley.

...Eastern Texas to Mississippi...
Aided by widespread precipitation across the cool sector, a cold
front is forecast to continue progressing towards the Texas coast
and Sabine Valley through the early morning hours. However, as one
or more weak shortwave impulses lifts northeast within the
sub-tropical channel, a slowly amplifying southerly low-level jet
should slow the southeastern advance of the combined front/outflow
boundary over northern Louisiana. Furthermore, broad forcing for
ascent may induce a weak surface low along this baroclinic zone
during the afternoon and evening hours. Within the warm sector
along/ahead of this frontal wave, surface dew points in the upper
60s are expected to foster upwards of 500-1000 J/kg of MLCAPE,
despite modest 700-500mb lapse rates. 

Thunderstorms should organize along the front, with some enhancement
in eastward propagation supported by any mergers from development
within moist/confluent flow in the open warm sector. A few small,
northeastward-advancing bowing segments may organize through the
afternoon and evening, owing to primarily uni-directional southerly
flow within the cloud-bearing layer. These cells will chiefly pose a
localized damaging wind threat. However, subtle backing of surface
flow near the front, combined with any northwest-southeast oriented
bands, may support a tornado or two as well.

..Picca/Leitman.. 02/21/2018

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SPC Feb 21, 2018 0700 UTC Day 2 Convective Outlook

SPC 0700Z Day 2 Outlook
      
Day 2 Outlook Image
Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1214 AM CST Wed Feb 21 2018

Valid 221200Z - 231200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Showers and a few thunderstorms are expected from Texas through a
portion of the Tennessee and Ohio Valleys Thursday.

...Texas into the lower Mississippi, Tennessee and Ohio Valleys... 

Upper pattern will remain characterized by a synoptic trough over
the western half of the U.S. Thursday. A low-amplitude shortwave
trough initially over the southern Rockies will eject northeast
through the Central Plains and middle MS Valley regions and undergo
deamplification in the process. Quasi-stationary front will reside
from the Middle Atlantic through the TN and lower MS Valleys to
south TX Thursday morning. This boundary may retreat some distance
northwest through the period. An ana-frontal southwesterly flow
regime will persist with episodes of showers and some thunderstorms
occurring, primarily within zone of isentropic ascent on the cool
side of the front. The elevated nature of the convection and weak
instability should preclude a threat for severe storms.

..Dial.. 02/21/2018

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SPC Feb 21, 2018 0830 UTC Day 3 Severe Thunderstorm Outlook

SPC 0830Z Day 3 Outlook
      
Day 3 Outlook Image
Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0145 AM CST Wed Feb 21 2018

Valid 231200Z - 241200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Showers and a few thunderstorms are expected from a portion of the
Southern Plains to the lower and middle Mississippi and Ohio Valley
regions Friday.

...Discussion...

Upper pattern will remain characterized by a synoptic trough over
the western U.S. and a downstream low-amplitude ridge in the east.
Weak vorticity maxima embedded within the broad southwesterly flow
regime will interact with baroclinic zone that should initially
extend from south TX into the OH Valley. Thunderstorms will likely
remain confined to zone of isentropic ascent and weak instability on
cool side of this front. Deep convection will struggle to develop in
warm sector due to weak forcing and a very marginal thermodynamic
environment including warming temperatures aloft.

..Dial.. 02/21/2018

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SPC Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook
          
Day 1 Fire Weather Outlook Image
Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0120 AM CST Wed Feb 21 2018

Valid 211200Z - 221200Z

...NO CRITICAL AREAS...

...Synopsis...
An upper trough will persist across the western U.S. while expansive
southwesterly flow encompasses much of the CONUS east of the
Rockies. A surface cold front will track eastward off the TX coast
and through New England, with the mid-South portion of the front
stalling from KY into the lower MS Valley region. Strong surface
high pressure will build over the Plains and Great Lakes behind the
front and generally moist conditions are expected from the southern
Plains into the southeastern U.S. A lack of strong surface winds
aligning with low RH conditions will preclude fire weather concerns
today.

..Leitman.. 02/21/2018

...Please see www.spc.noaa.gov/fire for graphic product...

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SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook
          
Day 2 Fire Weather Outlook Image
Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0120 AM CST Wed Feb 21 2018

Valid 221200Z - 231200Z

...NO CRITICAL AREAS...

...Synopsis...
The overall upper pattern will not change much on Day 2/Thursday.
The western upper trough will develop southward across the Great
Basin with southwesterly deep layer flow overspreading much of the
CONUS eastern of the Rockies. The stalled surface cold front will
slosh westward a bit, but generally remain draped from the Ohio
Valley into eastern TX. Some breezy conditions and marginally low RH
values will be possible ahead of the upper trough across parts of AZ
and NM, but fuel conditions are unfavorable and fire weather
concerns are not expected.

..Leitman.. 02/21/2018

...Please see www.spc.noaa.gov/fire for graphic product...

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