Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service northern Indiana
350 PM EDT Monday Apr 27 2015

issued at 702 am EDT Monday Apr 27 2015

High pressure over the upper Great Lakes will remain nearly
stationary the next few days as a low pressure system moves slowly
east from Texas to Georgia. This will result in fair weather across
our area. Temperatures will be below normal today with highs
in the middle 50s and lows tonight in the 30s with some frost
possible over southern Michigan and northern Indiana. Temperatures
should moderate back to near normal by Wednesday. An upper level
disturbance is expected to drop south across the area Thursday...
causing more cloudiness and possibly a few showers with slightly
cooler temperatures. The warmup should resume over the weekend as
the high pressure system moves to the southeastern U.S. Allowing
southwesterly flow and above normal temperatures to develop across
our area.


Short term...(this evening through tuesday)
issued at 350 PM EDT Monday Apr 27 2015

Cloud cover and associated impact on overnight lows/frost
potential are the main concerns for this short term period.
Cool/moist low level cyclonic flow in the wake of robust shortwave
diving through the eastern Great Lakes has led to a fair amount of
stratocu this afternoon. Low level flow does become more
anticyclonic overnight but forecast soundings indicate a decent
subsidence inversion around 850-700mb that will slow the diurnal
dissipation of present cloud cover. Still expect some clearing
overnight...especially in our western counties where clouds are
already scattered...but will take some time in our eastern County Warning Area
based on latest model relative humidity fields. This makes the precise overnight
lows difficult to predict...especially given weak pgf winds of 5
miles per hour or less. Latest consensus guidance is around middle 30s but a
degree or two in either direction will mean the difference between
frost or no frost. Stayed close to prior forecast of upper 30s in
the east and low/middle 30s in the west based on expected cloud
trends. Given light winds...clearing skies...and min temperatures in the
low-middle 30s...feel frost advisory is necessary for at least our
northwest third. Much lower confidence our east/southeast counties will
clear out and see any frost so will hold off on those for now and
just mention patchy frost. Later shifts can make adjustments
based on cloud/temperature trends overnight.

Another dry day on tap for tomorrow as middle/upper level ridging
slides over the Great Lakes. Another round of diurnal cumulus will lead
to just partly sunny skies during the afternoon but 850mb temperatures do
climb a degree or two above zero and this should allow highs to
reach the 60 degree mark.


Long term...(tuesday night through monday)
issued at 350 PM EDT Monday Apr 27 2015

Focus of the long term period is precipitation chances Wednesday night
through Thursday...and a warmer more active pattern next weekend.

Northern stream vorticity/jet maximum will dig southward from eastern
Manitoba/western Ontario Tuesday night through the Great Lakes
Wednesday/Wednesday night. Upper shortwave will deepen and cut off
over the Great Lakes region...which will then dig southeastward
towards the southeast Atlantic coast Thursday night...phasing with shearing
southern stream shortwave. As this low traverses almost directly
over the area...precipitation chances will increase late Wednesday through
Thursday. GFS has been most aggressive/deeper West/ Cutoff low
evolution than other models...however 12z European model (ecmwf)/NAM/Gem starting to
trend toward this more agressive solution. Therefore increased probability of precipitation
across the eastern half of the forecast area Wednesday night and
Thursday...and introduced slight chance probability of precipitation in the Wednesday period.

After this system moves southeast of the region Thursday
night...ridging will work eastward into the area on Friday...with
dry conditions and a warming trend into the weekend. Backed off with
slight chance probability of precipitation Friday night and Saturday...with an increase in
probability of precipitation into Sunday through sharp moisture increase across
the area and weak disturbances in quasi zonal flow will increase
precipitation chances. However...with weaker overall forcing
signal...will need to continue to watch this period for precipitation


Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 120 PM EDT Monday Apr 27 2015

Shortwave dropping south across the eastern Great Lakes is
generating a broken-overcast stratocu deck across southern Michigan and
Northeast Indiana. A brief period of high end MVFR conditions may
be possible at kfwa but latest observation and forecast soundings suggest
enough boundary layer mixing to keep ceilings above 3 kft. Clouds
will gradually scatter overnight as daytime heating ceases and dry
air/subsidence slowly build into the region. Another round of
diurnal cumulus expected tomorrow but ceilings look to remain VFR.


Iwx watches/warnings/advisories...
in...frost advisory from 2 am EDT /1 am CDT/ to 9 am EDT /8 am CDT/
Tuesday for inz003>006-012>016-020-022.

Michigan...frost advisory from 2 am to 9 am EDT Tuesday for miz077>080.

Lm...Small Craft Advisory until 8 PM EDT this evening for lmz043-046.



short term...agd

Visit US at www.Weather.Gov/iwx (all lower case)

Follow US on facebook...twitter...and youtube at:

National Weather Service Glossary of Abbreviations