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  Tuesday February 21, 2017

RSS Mesoscale Discussions from Storm Prediction Center

SPC - No watches are valid as of Tue Feb 21 18:42:01 UTC 2017

No watches are valid as of Tue Feb 21 18:42:01 UTC 2017.


No Mesoscale Discussions are in effect as of Tue Feb 21 18:42:01 UTC 2017.

SPC Feb 21, 2017 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1027 AM CST Tue Feb 21 2017

Valid 211630Z - 221200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for severe thunderstorms appears negligible across the
U.S., today through tonight.  Isolated thunderstorms are possible
from the lower Mississippi Valley region eastward along the Gulf
Coastal Plain, and from northern California to parts of Wyoming and
the northern High Plains.

...Lower Mississippi Valley and Eastern Gulf Coast...
Scattered thunderstorms are expected along with and in advance of an
upper low that will move eastward along the Gulf Coast this
afternoon and tonight. Cold temperatures aloft will support some
small hail across portions of southern LA this afternoon as modest
heating/destabilization occurs, though low tropopause heights in the
vicinity of the upper cyclone will limit the depth of convection and
preclude any substantial severe hail risk. 

...Northern CA/Southern OR into the Great Basin/Northern Rockies...
As an upper trough approaches the Pacific Coast, generally weak
convection is expected across a broad area from the northern
CA/southern OR coast eastward into the Great Basin and Northern
Rockies, with isolated thunderstorms possible where convection
becomes sufficiently deep. Somewhat greater instability across
portions of the northern CA coast into the northern Sacramento
Valley may support some thunderstorms capable of small hail and
locally gusty winds, though generally weak effective shear
magnitudes should limit storm organization. 

...Portions of the Northern High Plains...
A shortwave trough over portions of the Northwest will move quickly
into the northern High Plains this afternoon and evening. Ahead of
this feature, weak but sufficient instability will support
fast-moving clusters of convection later this afternoon and tonight
from central/eastern MT into ND. Relatively strong low/midlevel flow
and effective shear may support locally gusty winds and perhaps some
small hail with the strongest of these clusters.

..Dean/Guyer.. 02/21/2017

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SPC Feb 21, 2017 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook
      
Day 2 Outlook Image
Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1122 AM CST Tue Feb 21 2017

Valid 221200Z - 231200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe weather is not expected across the contiguous United States
on Wednesday.

...Synopsis...
A belt of enhanced west/southwesterly mid-level flow will stretch
from southern/central California to the Upper Midwest during the
day, as a trough continues to overspread the Pacific Northwest.
Farther east, another impulse will translate eastward from the
northern Plains to the upper Great Lakes. Across the southeastern
US, a weakening mid/upper low will cross the Florida peninsula late
in the period. The surface response will feature a cold front
gradually progressing southward over portions of the southern Great
Basin, while another front pushes southeastward across the northern
Plains and Upper Midwest.

...Florida Peninsula...
Despite the weakening nature of the mid/upper low, cooling aloft and
increasing low-level moisture will support enough buoyancy for
scattered thunderstorms across the peninsula during the day.
Relatively weak low-level flow and marginal buoyancy are expected to
preclude a threat of severe thunderstorms.

...Pacific Northwest...
Cold mid-level temperatures (around -34 to -38 C) will come ashore
the coast during the period. Despite cool surface conditions and low
dew points, steep low/mid-level lapse rates should encourage the
development of isolated thunderstorms during the afternoon.

..Picca/Broyles.. 02/21/2017

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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
1051 AM CST Tue Feb 21 2017

Valid 211700Z - 221200Z

...CRITICAL FIRE WEATHER AREA FOR COLORADO FRONT RANGE...

Critical fire-weather conditions are expected across much of the
front range of eastern Colorado. Surrounding the critical, elevated
fire-weather conditions are expected across much of the central
Great Plains.

Observations suggest that overnight relative humidity recovery was
poor across much of the Colorado Front Range. This coupled with
downslope flow will allow for warm/dry conditions in the presence of
gusty surface winds. As such, only slight changes were made to the
previous critical area.

To the north of the critical, stronger low-level winds are expected.
However, relative-humidity values are only expected to fall into the
15-30% range, which should temper the magnitude of the fire-weather
threat. Given the combination of strong, gusty winds and dry fine
fuels an elevated fire-weather threat is expected.

To the east of the critical, across portions of Nebraska and Kansas,
minimum relative-humidity values are expected to also fall into the
15-25% range. Winds should be weaker across this area as compared to
areas to the north and west, but the ongoing dry conditions and
potential for gusty surface winds will support at least elevated
fire-weather conditions.

To the south of the critical, across southern Colorado and far
northeast New Mexico, minimum relative-humidity values should fall
into the upper-single digits to low teens. Although relative
humidity will be well within critical thresholds, surface wind
should be somewhat less as compared to farther north. This should
temper the overall fire-weather threat, although elevated
fire-weather conditions are still expected.

..Marsh.. 02/21/2017

.PREV DISCUSSION... /ISSUED 0156 AM CST Tue Feb 21 2017/

...Synopsis...
An extensive midlevel wind-speed maximum is forecast to overlie
areas from coastal CA to the upper MS Valley, while mean troughing
is reinforced over the Pacific Northwest and adjacent east Pacific.
A surface trough will deepen over portions of the northern and
central High Plains. Two separate regions of fire-weather highlights
are in effect, as subsequently discussed, while recent precipitation
between and north of these areas may limit the fire-weather risk.

...Portions of southeast WY, northeast CO, western NE...
Enhanced downslope winds extending off the central Rockies will
support warming/drying over the adjacent High Plains. Westerly winds
of 15-25 mph with higher gusts are forecast to combine with RH
around 12-20 percent in support of elevated to critical fire-weather
conditions.

The latest short-range, high-resolution model guidance suggests that
overlap of critically strong winds (speeds of 20-25 mph) and low RH
(12-15 percent) will be most likely for the following areas: the
vicinity of the CO Front Range and surrounding foothills, eastward
across portions of the northeastern CO High Plains, extreme
southeast WY, and extreme southern parts of the NE Panhandle. Given
relatively limited precipitation across these areas, sufficiently
dry fuels exist for Critical designation.

For locations surrounding the Critical area, elevated to
borderline-critical fire-weather conditions will be possible,
warranting Elevated designation. However, the strongest winds are
forecast to remain displaced to the north of the lowest RH, limiting
the critical fire-weather potential.

...Portions of southwest KS northeastward to south-central NE...
A modestly enhanced low-level pressure gradient east of the lee
trough is forecast to support southwesterly to west-northwesterly
surface winds of 15-18 mph. With a warm air mass in place and a
dearth of moisture return, vertical mixing will encourage RH values
falling to around 12-20 percent. While elevated fire-weather
conditions are expected, critically strong winds are unlikely.

...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
1237 PM CST Tue Feb 21 2017

Valid 221200Z - 231200Z

...CRITICAL FIRE WEATHER AREA FOR FRONT RANGE OF EAST COLORADO AND
NORTHEAST NEW MEXICO...

Latest guidance continues to support another critical fire-weather
day across portions of the east Colorado and northeast New Mexico
Front Range. Strong downslope flow will contribute to warming/drying
of the airmass with afternoon temperatures in the 60s and minimum
relative humidity in the low teens.

To the north, east, and south of the critical, elevated fire-weather
concerns will remain. In these surrounding areas, surface-wind
speeds look to remain below critical thresholds (15 miles per hour),
despite relative-humidity values approaching and falling below
critical thresholds (15%). Thus, elevated fire-weather conditions
look likely.

..Marsh.. 02/21/2017

.PREV DISCUSSION... /ISSUED 0157 AM CST Tue Feb 21 2017/

...Synopsis...
In the mid levels, a trough will amplify over the Western States,
and will be accompanied by a belt of strong flow spreading across
parts of the Southwest to the central and southern Plains. As the
leading edge of this stronger flow and associated large-scale ascent
emerge over parts of the central and southern Rockies, a lee surface
trough will deepen across parts of the adjacent High Plains.

...Front range of the CO/NM Rockies eastward across portions of the
central/southern High Plains...
Enhanced downslope winds extending off portions of the central and
southern Rockies will support warming/drying over the adjacent High
Plains. Westerly to west-southwesterly winds of 15-25 mph with
higher gusts are forecast to combine with RH of 10-20 percent in
support of elevated to critical fire-weather conditions.

The latest model guidance suggests that overlap of critically strong
winds (speeds of 20-25 mph) and low RH (10-15 percent) will be most
likely across portions of eastern CO, northeast NM, and the western
TX and OK Panhandles. 

Surrounding the Critical area, elevated to borderline-critical
fire-weather conditions will be possible, warranting Elevated
designation. However, critically strong winds are not forecast to
combine with critically low RH on any more than a brief/spotty
basis.

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

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