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SPC Mesoscale Discussions



Storm Prediction Center



Published: Wed, 18 Jan 2017 01:10:01 +0000

Last Build Date: Wed, 18 Jan 2017 01:10:01 +0000

Copyright: None
 



SPC MD 66

Wed, 18 Jan 2017 01:09:02 +0000

MD 0066 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR COASTAL PLAIN OF TEXAS
(image)

Mesoscale Discussion 0066
NWS Storm Prediction Center Norman OK
0708 PM CST Tue Jan 17 2017

Areas affected...Coastal plain of Texas

Concerning...Severe potential...Watch unlikely 

Valid 180108Z - 180315Z

Probability of Watch Issuance...20 percent

SUMMARY...Marginal severe hail and perhaps a tornado can be expected
along a frontal zone over the coastal plain of Texas this evening. 
Tornado watch is not anticipated at this time.

DISCUSSION...Sustained low-level warm advection appears to be the
primary forcing mechanism for slowly maturing thunderstorms across
the western coastal plain of TX.  Over the last hour or so
convection has gradually deepened over Webb/Duval/Jim Hogg counties
and updrafts are now producing lightning within several clusters. 
00z sounding from CRP is very moist with PW on the order of 1.75
inches and surface dew points across the warm sector are in the
lower 70s.  While low-level shear is not that strong...more than
adequate deep-layer flow exists across this region for sustaining
rotating updrafts.  There is some concern that a few supercells will
evolve near the quasi-stationary frontal zone and this low-level
feature may locally enhance the possibility for a tornado along a
corridor from Jim Hogg county, northeast toward Matagorda county
this evening.  At this time it appears the severe coverage will be
too sparse to warrant a tornado watch.

..Darrow/Thompson.. 01/18/2017

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

ATTN...WFO...HGX...CRP...BRO...

LAT...LON   27629904 28689728 29149619 28749588 27509744 26979866
            27629904 

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SPC MD 65

Wed, 18 Jan 2017 00:00:03 +0000

MD 0065 CONCERNING FREEZING RAIN FOR PORTIONS OF NORTHWEST OREGON AND SOUTHWEST WASHINGTON
(image)

Mesoscale Discussion 0065
NWS Storm Prediction Center Norman OK
0542 PM CST Tue Jan 17 2017

Areas affected...Portions of northwest Oregon and southwest
Washington

Concerning...Freezing rain 

Valid 172342Z - 180545Z

SUMMARY...Moderate to locally heavy freezing rain rates are possible
into the evening from the central/northern Willamette Valley through
the Columbia River Gorge into adjacent parts of the Cascades.

DISCUSSION...At 2330Z, the leading edge of a substantial
precipitation shield is moving into western Oregon and Washington. A
continuous feed of moisture ahead of an upper trough off of the
Pacific Northwest coast will maintain moderate to locally heavy
precipitation rates through tonight. Meanwhile, drainage of cold air
from the east through the Columbia Gorge is maintaining subfreezing
temperatures from the southern WA Cascades westward to the
central/northern Willamette Valley. The KPDX ASOS site has reported
0.20 inches of ice accretion over the last two hours, with nearby
sites reporting at least 0.05 inch-per-hour rates. Rates of
0.05-0.10 inches per hour will spread eastward with time this
evening, leading to significant ice accumulations. 

Some erosion of the shallow subfreezing layer is possible this
evening across the western portion of the MCD area, including the
Portland metro area. However, with a relatively strong pressure
gradient being maintained and very cold temperatures across portions
of eastern Washington and northeast Oregon, temperatures will be
very slow to rise as strong easterly flow through the Gorge
continues.

..Dean.. 01/17/2017

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

ATTN...WFO...PDT...PQR...

LAT...LON   45712314 46002288 46082264 45852229 45862196 46132127
            46282094 46302061 45692049 45492062 45452123 45522152
            45522176 45512199 45452221 45392240 45302269 45172311
            45422320 45712314 

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