Area forecast discussion
National Weather Service northern Indiana
635 am EDT sun may 19 2013
Synopsis...
issued at 620 am EDT sun may 19 2013
A weak upper low will eject northeast today...with a shower or
thunderstorm possible over mainly Ohio. Otherwise...an upper level
ridge will build northeast across the Midwest into the Ohio Valley
region early this week. Temperatures will become hot by Monday with
highs around 90. As the upper level ridge builds east...showers and
thunderstorms will spread east in advance of a cold front and
upper level disturbance Monday through Thursday. Rainfall amounts
should exceed an inch by late in the week.
&&
Short term...(today and tonight)
issued at 503 am EDT sun may 19 2013
An upper low south of the area will eject east out of the region
today. In its wake...a lingering surface dew point gradient was
still over the area...but not as pronounced as the last couple of
nights. Concern with daytime heating and afternoon/early evening
convective available potential energy topping 3000 j/kg per NAM buf/kit over southwest areas.
However... the environment will remain very lightly sheared with
really nothing to focus or force convection...other than the
modifying dew point boundary. For now...kept showers/storms out of
the forecast today. Kept a low chance for showers/storms tonight over northwest
areas with the approach of an embedded short wave trough in the
approaching long wave trough...and also in the vicinity of an areas of
low level Theta-E convergence. Otherwise...kept highs today above
even the warmer GFS/mav with 850 mb temperatures pushing 17c with
increasing upper level subsidence.
&&
Long term...(monday through saturday)
issued at 503 am EDT sun may 19 2013
Negatively tilted longwave trough currently over the Rocky Mountains
will fully transition to an expansive closed low by Monday and will
bring increasing chances for showers and thunderstorms in our area
through midweek as it very slowly progresses eastward. Precipitation
chances on Monday still a bit of a question mark though. Surface
frontal boundary will be well north of here by Monday afternoon with
good southwest flow pushing 850mb temperatures to around 19c. Mixing this
to the surface yields afternoon temperatures approaching 90f...in line with
a consensus of latest MOS guidance. Not unheard of to reach 90f this
early but certainly not common. Surface dewpoints will also be
creeping into the middle and perhaps upper 60s. 70f dewpoints seen in
raw guidance likely a bit overzealous but modified soundings still
show a healthy amount of conditional instability. Question continues
to be how strong the cap will be over our area. Southern Great Lakes
continue to be largely under the influence of midlevel ridging on
Monday and the associated anticyclonic vorticity should favor a
decent subsidence inversion...at least early in the day. Potential
exists for midlevel height falls to push far enough east by late in
the day to allow for convective initiation and downstream
propagation...as seen in newest 00z NAM...but still feel that
largely cutoff nature to upstream height anomaly favors slower
progression seen in the latest GFS solution. Will therefore maintain
relatively low probability of precipitation during the day with the best chance across the
northwest during the late afternoon/early evening. Chances increase
Post 00z as decaying convection eventually spreads east but lack of
good synoptic forcing may limit coverage/amounts after the loss of
daytime heating. Severe weather remains possible if convection
arrives early enough. Shear values are less than stellar but do
increase in the west by the end of the day. This coupled with good
diurnally driven instability warrants continued conditional threat.
Precipitation chances/coverage will increase heading into Tuesday and Wednesday as
the vertically stacked low gradually approaches the Great Lakes.
Broad warm/moist air advection will support widespread showers and
thunderstorms across the entire region. Also expect several midlevel
waves to ripple through the region and enhance precipitation
coverage/intensity but exact timing and location will depend on
mesoscale details impossible to resolve at this time range. Timing
of these mesoscale features will also impact our severe weather
chances. Any break in precipitation on Tuesday could allow for enough
diurnal instability to support severe weather given decent wind
profiles but forecast soundings show increasingly moist adiabatic
lapse rates that will likely inhibit our severe chances...especially
by Wednesday. Significant disagreement between European model (ecmwf) and GFS on how
quickly upper low gets reabsorbed into mean flow. This will have a
large impact on precipitation chances Thursday but expect there will be at
least some residual showers in the wake of departing low. Northwest
flow will return by Friday with cool and dry conditions expected for
at least the first half of the weekend.
&&
Aviation...(for the 12z tafs through 12z Monday morning)
issued at 620 am EDT sun may 19 2013
A tight moisture gradient remained over the area...with dew
points much higher just south of the terminals. Afternoon convective available potential energy
of 2000 to 3000 j/kg would support convection...but given light
wind fields and nothing to force or focus convection...kept tafs
dry with VFR conditions. Winds should remain east to southeast
under 10 knots.
&&
Iwx watches/warnings/advisories...
in...none.
Michigan...none.
Ohio...none.
Lm...none.
&&
$$
Synopsis...marsili/kg
short term...skipper
long term...agd
aviation...skipper
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