Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gaylord Michigan
133 PM EDT Tuesday Jul 22 2014
issued at 354 am EDT Tuesday Jul 22 2014
Very warm and humid conditions can be expected today out ahead of a
slowly approaching cold front. In addition...showers and
thunderstorms are possible later today into tonight as the front
moves into the region. Cooler and much less humid conditions are
then expected Wednesday into the end of the week. There will be
chances for showers and thunderstorms this weekend as a trough
approaches the region.
issued at 1043 am EDT Tuesday Jul 22 2014
Challenging but fun convective forecast as we head into the
afternoon and evening hours...with a note that the going forecast
doesn't look too shabby...though have pushed back timing of precipitation
chances later into the afternoon. Early morning analysis shows a
rather healthy convectively-enhanced shortwave skirting Northwest
Lake Superior at the moment...tied to an earlier axis of severe
convection that originated late yesterday over North Dakota. That
stuff has continued to work east but has faded rapidly upon
approach of the eastern u.P. As it has outrun all available
instability...running instead into a heavily capped environment
down this way (see 12z apx/grb raobs). All the while...a modest
cold front is laid out from Western Lake Superior down into
southern Nebraska...with this feature of most interest for US as
we push through the afternoon/evening hours.
Early into the afternoon...can't rule out a smattering of showers
(isolated thunder) redeveloping toward the eastern u.P. Ahead of
the shortwave shearing out into southern Ontario. However...the
better chance should wait until the cold front approaches in the
20-23z time frame. Quite the strong capping in the 850-700mb layer
to overcome...and would really like to see some semblance of
better upper forcing to help erode this cap. With that said...
suspect decent lower level convergence will prove sufficient to
lift parcels just up and over the warm layer...likely beginning
just downwind of Lake Michigan...as quickly veering boundary layer
flow profiles to the west likely help "shadow out" areas near the
lake. From an instability standpoint...things look better than
yesterday...with a more easterly displaced elevated mixed layer
helping bump mixed layer cape values up toward 2000 j/kg...
particularly down south of M-72 where surface dew points should
climb well into the 60s/near 70 in the pre-frontal environment.
The big question is just how quickly we can erode the cape...with
only a narrow window to do so before markedly drier air arrives
through the evening hours.
Shear profiles look OK...but mainly confined below 500mb with
effective shear values up around 30 knots. Given high freezing
levels/only modest shear...hail doesn't look like a huge threat
but it's possible with any stronger cores. A wind damage threat
could exist with a better core of wind prognosticated between 850-700mb
(up to around 35-40 knots)...but we will need some fairly strong
storms do to the trick. All in all...confidence is moderate that
at least scattered convection will develop...primarily after
21-22z...but severity and ultimate coverage is still something
that will be watched closely.
Short term...(today through tonight)
issued at 256 am EDT Tuesday Jul 22 2014
..a couple of chances for thunderstorms...
Impacts: lightning from thunderstorms. Severe threat minimal...but
main threat is wind. Great Lakes fog.
Current weather and synoptic pattern:
Now we are starting to get closer to all the action...after several
days of increasingly more Summer-like weather. Looking at upstream
conditions...more Summer can be expected heading through today and
tonight. Across northern Minnesota resides a potent little shortwave/vorticity maximum
and associated surface low pressure...with a cold front draping SW and
into SD/NE. Ahead of this front and surface low...is a 40-50kt 800 mb low level jet
and axis of maximum Theta-E/instability. An mesoscale convective system was earlier producing
sporadic damaging winds (50kt middle level jet) while feeding on this
moisture and instability. However...the storm complex was weakening
as it has encountered a more capped atmosphere to its east in
Wisconsin. The 00z apx sounding shows our strongly capped
atmosphere...maxed around 750mb. We were very mild with continued
low to middle level warm advection. Even with clear skies...all areas
were basically in the 60s.
Synoptic pattern/weather evolution:
Through morning...we do continue to moisten the low levels...but
best Theta-E advection and low level jet forcing all lift to our north.
Considering the strong capping in place...gotta believe that the
upstream mesoscale convective system will not affect northern lower...but maybe some remnant
showers/storms can roll through eastern upper. This is pretty low
chance though. The shortwave will want to shear out and track a bit
further north into the day...while dragging the surface cold front into
eastern upper around 21z and across northern lower 00-03z. This is the
right time for peak heating/maximum instability...which ranges from
several hundred j/kg north...to as much as 1800 j/kg south. Pure
diabatic heating doesn't look to get past the cap...but with the
arrival of the front and shortwave...can buy into scattered showers
and some storms rolling on through. Most of the instability will be
well south and west of US...and would really like to see some better
cooling/steeper lapse rates aloft. The shearing out wave doesn't
help much here. There are definite differences in data between how
much of the cap can be eroded...some data suggesting that the cap
plays a major role in really limiting what we can attain as far as
convection. A more realistic idea with this setup/environment is for
at least some scattered activity along and ahead of the front with
just an outside shot at some damaging winds...and to a lesser degree
severe hail. Once again...it appears as though the amount of
instability will will not be enough to generate strong enough
updrafts to support any significant hail...or to tap into rather
minimal 40-45kt middle level winds. Severe threat is minimal.
Front clears NE lower/sag Bay area around 03z....with strong drying
and cooling behind it. Northerly flow to near 750mb with precipitable waters
falling from 1.70" to near 0.50". Should clear pretty well with
maybe some scattered lower clouds (fcst before soundings suggest more
solid stratus...but this is doubtful).
High temperatures in the lower 80s eastern upper/85-90 in northern lower. Lows
tonight low 60s southeast...but falling into the 50s elsewhere.
Long term...(wednesday through monday)
issued at 354 am EDT Tuesday Jul 22 2014
..cooler and much less humid weather on the way...
High impact weather potential: very low.
Breezy...cooler and much less humid conditions are expected behind
the departing cold front on Wednesday. Meanwhile...surface high
pressure builds in through Thursday. This will lead to mostly clear
skies and diminishing winds Wednesday night. The high will slip off
to our east Friday leading to a somewhat milder southwest flow.
Extended models then vary on a possible short wave approaching from
the west on Saturday...so will continue with low chance probability of precipitation. The
bigger story over the next several days will likely be a deepening
upper level long wave trough which is shown to dig into the Great
Lakes region Sunday into the beginning of next week. This system if
it comes to fruition would spell cooler and unsettled conditions. In
fact...temperatures through the period are expected to be at least a
few degrees below average for late July. Highs in the upper 60s to
middle 70s Wednesday...the lower to middle 70s Thursday then the
middle to upper 70s Friday through Sunday followed by the upper 60s
to middle 70s Monday. Lows in the cooler middle 40s to middle 50s
for both Wednesday and Thursday nights then the middle to upper 50s
over the weekend.
Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 333 PM EDT Tuesday Jul 22 2014
A cold front is making its approach...with a quick round or two of
thunderstorms possible for the terminal sites into early evening.
Some lower stratus clouds may also sneak into the picture before
those storms occur...particularly up near the pln area where
ceilings may dip into the MVFR range. A period of clearing is
expected for a time as the front passes...before some lower
stratus redevelops for many areas later tonight. Winds will remain
gusty from the southwest right on through early evening...gusting
to around 25 knots at times...shifting northwest and then north
late tonight into Wednesday.
issued at 256 am EDT Tuesday Jul 22 2014
Low pressure and a cold front will cross the nearshore waters this
afternoon through this evening. The pressure gradient strengthens
ahead of the front and is the reason for the Current Lake Michigan
advisories. This still looks good with 35-40kts S/SW flow off the
surface...despite stability concerns. More advisories now posted through
Wednesday morning for the remainder of the nearshores. This is due
to strong cold advection/slightly unstable conditions developing...a
period of 30-35kt northwest/north low level winds just above the water
surface...and resultant choppy waves.
Winds weaken and back more westerly into Thursday as high pressure
begins to settle in.
LH...Small Craft Advisory from 5 PM this afternoon to 2 PM EDT
Wednesday for lhz345>349.
Lm...Small Craft Advisory from 5 PM this afternoon to 2 PM EDT
Wednesday for lmz323.
Small Craft Advisory until 2 PM EDT Wednesday for lmz341-342-
Ls...Small Craft Advisory from 5 PM this afternoon to 2 PM EDT
Wednesday for lsz321-322.