- Day Three
acus01 kwns 010600
Storm Prediction Center ac 010559
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
1259 am CDT Wednesday Jul 01 2015
Valid 011200z - 021200z
..there is a slight risk of severe thunderstorms MO to the Tennessee Valley...
..There is a marginal risk of severe thunderstorms northern/Central High plains to the
..there is a marginal risk of severe thunderstorms northeast / New England...
..There is a marginal risk of severe thunderstorms Arizona...
Scattered severe storms with a couple tornadoes...large hail...and
damaging winds are expected across parts of Missouri in the late
afternoon and evening. Storms with scattered damaging winds are
probable midday into the afternoon across the Tennessee Valley.
Upper trough over the lower Great Lakes to central Appalachians will
progress across the northeast into New England through this
afternoon with low-amplitude vorticity maxima persisting upstream
across Ontario/Great Lakes. These will help maintain a broad
cyclonic flow regime over much of the central/eastern Continental U.S. With several
embedded minor middle-level impulses from the southern Canadian rockies to
the Tennessee Valley. A Stout upper anticyclone will remain anchored over
the eastern Great Basin.
An mesoscale convective system will be ongoing at 12z aided by robust low-level warm air advection. While
this activity will diminish...in its wake...residual convective
outflow amidst intense diabatic heating over Kansas should yield a
strengthening baroclinic zone. With around 70 degree surface dew
points...a corridor of moderate to large buoyancy will likely
develop. Convection should form over parts of western MO by late
afternoon. Veering winds with height should result in effective
shear around 40 knots...aiding in a few supercells with large hail and
tornadoes possible. Convection should grow upscale into an mesoscale convective system in
the evening as a southwesterly low level jet intensifies with the risk transitioning to
Low-level moisture advection from the lower MS valley in conjunction
with strong diabatic heating should result in moderate to large
buoyancy developing downstream of an mesoscale convective system expected to be ongoing at
12z over MO. While this mesoscale convective system may decay for a time...remnant
southeastward-propagating outflows should Foster surface-based development
around midday. While deep-layer shear should be modest...one or more
multicell clusters should form with damaging winds as the main
..nrn Great Plains...
A weak shortwave impulse over southern British Columbia should reach the
Saskatchewan/Mt/ND border area at 02/00z. This should aid in
isolated thunderstorms despite a nebulous surface pattern and predominately
northerly low-level winds. But within a belt of moderate to strong
middle-level nwlys...30-40 knots effective shear could Foster a couple
supercells producing severe hail/wind. Given the lack of surface
focus and low confidence in thunderstorm coverage...will maintain marginal
risk probabilities this outlook.
Current convection from eastern New York to eastern Virginia will likely be ongoing at
12z across mainly southern New England. The strongest shear profiles will
exist in the morning...but surface-based instability should be quite
limited. Scattered diurnally driven thunderstorms should form across parts
of New York into western New England in the afternoon beneath the middle-level
thermal trough. While the combination of buoyancy and shear should
remain modest...stronger updrafts will be capable of marginally
severe hail and localized damaging winds.
In the wake of relatively widespread convection currently...guidance
is fairly consistent in suggesting both weaker middle-level elys and
warmer middle-level temperatures this afternoon/evening. This suggests
the degree of convection will be suppressed relative to recent days.
Still...sufficient buoyancy/shear should exist for a risk of severe
wind gusts with perhaps only isolated convection over the higher
acus11 kwns 010854
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 010854
Mesoscale discussion 1263
National Weather Service Storm Prediction Center Norman OK
0354 am CDT Wednesday Jul 01 2015
Areas affected...Long Island / far southern New York / CT / Rhode Island
Concerning...severe potential...watch possible
Valid 010854z - 011000z
Probability of watch issuance...40 percent
Summary...line of storms over the lower Hudson Valley will move northeastward
across Long Island and CT and potentially yield an isolated
wind-damage risk as the squall line organizes further.
Discussion...radar mosaic over the past hour has shown a
consolidation of line segments into a larger-scale convective line
over the lower Hudson Valley and areas S of NYC. Water vapor
imagery shows a potent upstream shortwave trough over the central
Appalachians becoming negatively tilted this morning. The
increasing larger-scale forcing for ascent and strengthening
middle-tropospheric southwesterly flow --sampled by the okx VAD from 35 to 55
knots-- over the past few hours will support convective line longevity.
Surface analysis places a wedge of higher Theta-E characterized by
temperatures in the lower 70s with middle-upper 60s dewpoints over Long Island
into much of CT. To the north over Massachusetts...warmer/more moist
boundary-layer air will probably not penetrate the area as the
convective line will outrun the northward advancement of a slow-moving
warm front draped over southern New England. Relatively drier air above
the near-surface layer may act to enhance or reinforce wind gust
potential. As a result...strong to severe straight-line winds
/gusts 40-60 miles per hour/ may yield isolated wind damage across southern New
England over the next few hours.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 41267389 41797354 42077292 42037210 41707162 41377143
40977188 40507359 41267389