Jul 9, 2017 1630 UTC Day 1 Convective Outlook
Updated: Sun Jul 9 16:34:15 UTC 2017 (20170709 1630Z Day 1 shapefile | 20170709 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170709 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 35,235 4,746,420 Minneapolis, MN...St. Paul, MN...Rochester, MN...Bloomington, MN...Plymouth, MN...
SLIGHT 69,596 15,627,445 Chicago, IL...Milwaukee, WI...Madison, WI...Aurora, IL...Rockford, IL...
MARGINAL 337,643 30,033,404 Houston, TX...Dallas, TX...Austin, TX...Fort Worth, TX...Tucson, AZ...
Probabilistic Tornado Graphic
20170709 1630 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
2 % 49,615 5,080,720 Minneapolis, MN...St. Paul, MN...Rochester, MN...Bloomington, MN...Plymouth, MN...
Probabilistic Damaging Wind Graphic
20170709 1630 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
30 % 34,955 4,828,373 Minneapolis, MN...St. Paul, MN...Rockford, IL...Rochester, MN...Bloomington, MN...
15 % 68,166 15,354,196 Chicago, IL...Milwaukee, WI...Madison, WI...Aurora, IL...Naperville, IL...
5 % 339,350 29,965,243 Houston, TX...Dallas, TX...Austin, TX...Fort Worth, TX...Tucson, AZ...
Probabilistic Large Hail Graphic
20170709 1630 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SIG SEVERE 20,590 3,407,734 Minneapolis, MN...St. Paul, MN...Bloomington, MN...Plymouth, MN...Brooklyn Park, MN...
15 % 87,532 8,491,922 Minneapolis, MN...St. Paul, MN...Madison, WI...Rockford, IL...Cedar Rapids, IA...
5 % 169,319 15,367,489 Chicago, IL...Milwaukee, WI...Des Moines, IA...Aurora, IL...Naperville, IL...
   SPC AC 091634

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1134 AM CDT Sun Jul 09 2017

   Valid 091630Z - 101200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER THE UPPER
   MISSISSIPPI VALLEY REGION...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   ENHANCED RISK OVER THE UPPER MIDWEST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE UPPER
   MIDWEST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM COASTAL
   CAROLINAS INTO SOUTHERN GEORGIA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER SOUTHERN
   ARIZONA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE
   NORTHERN ROCKIES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM TEXAS TO
   THE LOUISIANA COAST...

   ...SUMMARY...
   Severe thunderstorms are expected late this afternoon into tonight
   across the Upper Midwest, particularly across central and southern
   Minnesota, northeast Iowa, southwest Wisconsin and northwest
   Illinois. Strong thunderstorms may also impact portions of the south
   Atlantic coast into southern Georgia, southern Arizona, and portions
   of the northern Rockies this afternoon and evening.

   ...Upper Mississippi Valley region...
   Morning clouds and scattered weak convection over parts of the upper
   Midwest are associated with a lead short wave trough moving across
   the area.  This is expected to shift eastward over the next few
   hours in advance of a stronger perturbation evident in water vapor
   imagery moving southeastward over far southern Manitoba.  This
   latter feature is forecast to progress into the upper Mississippi
   Valley this afternoon and tonight contributing to an increased risk
   of severe storms that will continue through much of the overnight
   hours.

   Low-level moisture is expected to increase northward into the region
   this afternoon and evening as a southwest low-level jet strengthens
   from western Iowa into southern Minnesota.  A plume of steep
   mid-level lapse rates is forecast to spread into the upper
   Mississippi Valley this afternoon and contribute to an increasingly
   unstable environment by later this afternoon and evening with MLCAPE
   of 1500-3000 J/kg in place into the region.

   Model guidance suggests the cap associated with the EML plume will
   delay primary storm development until late this afternoon and
   evening over parts of central Minnesota.  Strong veering wind
   profiles with height associated with the southwesterly low-level jet
   and northwest flow in the mid/upper levels will result in 40-50 kt
   deep layer shear, supportive of supercell characteristics in initial
   discrete storms.  Very large hail and a tornado or two will be
   possible.  With time the activity is expected to grow upscale into
   one or two bowing QLCS systems that will accelerate southeastward
   into the overnight hours.  The primary severe risk is expected to
   evolve into primarily a damaging wind threat tonight with potential
   for one or more swaths of wind damage occurring across the immediate
   Mississippi Valley region.  A severe threat may persist through much
   of the overnight hours and the severe risk areas have been extended
   southeastward into northern parts of Illinois and Indiana to reflect
   this scenario.

   ...Southern Arizona...
   A modest weakening of the Four Corners vicinity upper-level ridge is
   forecast today with expectations for somewhat weaker easterly
   steering flow, in addition to what may be sub-optimally timed
   ridge-peripheral disturbances. Even so, where isolated storms do
   develop/slowly propagate this afternoon and evening, a hot/deeply
   mixed boundary layer will support the possibility of locally strong
   wind gusts and blowing dust, mainly across parts of
   southern Arizona.

   ...Coastal portions of the Carolinas and Georgia...
   Along and east of a weak slow-moving/stalling front, a moist air
   mass featuring 70s F surface dewpoints and ample precipitable water
   (in excess of 2 inches) will linger today mainly in coastal areas of
   the Carolinas and southern Georgia.  Heating and front/sea
   breeze-related convergence aside, thunderstorm development will be
   favorably influenced by cyclonic flow aloft. While
   low/mid-tropospheric winds will be weak (less than 20 kt),
   sufficiently steep low-level lapse rates and ample moisture
   conducive for water loading could yield some strong to locally
   severe downdrafts this afternoon/early evening.

   ...Portions of southern Plains/Ark-La-Tex to the Gulf Coast...
   Pockets of locally stronger heating/destabilization should occur
   today near and south of a convectively modulated/decaying front.
   While overall forcing for ascent and vertical shear will remain
   weak, sufficient moisture/destabilization could allow for a few
   instances of downbursts capable of very localized wind damage. 

   ...Northern Rockies...
   A western states ridge-peripheral disturbance, in addition to height
   falls over the Pacific Northwest, should influence thunderstorm
   development across the region aside from adequate moisture and
   orographic lift. Storms should initially develop and intensify this
   afternoon across eastern Idaho/southwest Montana into western
   Wyoming. Adequate moisture/buoyancy in the presence of as much as
   25-35 kt of effective shear could yield a few instances of
   marginally severe hail, while a relatively warm/well-mixed boundary
   layer could support severe downdrafts this afternoon through early
   evening.

   ..Weiss/Dial.. 07/09/2017

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