Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kiwx 212330 

Area forecast discussion
National Weather Service northern Indiana
730 PM EDT Sat Sep 21 2019

issued at 348 PM EDT Sat Sep 21 2019

Expect increasing chances for showers and thunderstorms in the
northwest tonight into Monday morning. The best chances will be
Sunday afternoon and Sunday night as a cold front passes through the
forecast area. Heavy rain is possible, especially west of Highway
31. Hazardous swimming conditions are expected on Lake Michigan
tonight and Sunday. Low temperatures tonight will be in the 60s.
High temperatures Sunday will be in the mid to upper 70s near Lake
Michigan, and in the low to mid 80s elsewhere. Dry conditions return
Monday afternoon into Wednesday morning.


issued at 729 PM EDT Sat Sep 21 2019

Minor adjustments to the forecast to handle sprinkles/light rain a
bit better moving across central portions of the area with
remainder of forecast on track for the time being.

Some concerns that further tightening of pops/quantitative precipitation forecast may be needed
into the overnight hours based on upstream trends which show the
bulk of the precip only impacting LaPorte/Berrien counties. Not
ready to change yet, as some cams do suggest an uptick on coverage
overnight that could extend to the US-31 corridor. Will continue
to monitor.


Short term...(this evening through sunday)
issued at 348 PM EDT Sat Sep 21 2019

Main focus for the short term is precipitation chances tonight into
Monday morning. Scattered showers and isolated storms in the
northeast will gradually diminish this evening. Focus then turns to
the next system. Generally speaking, I tightened the pop/quantitative precipitation forecast
gradient a little bit more in line with latest model trends, with
highest totals in southwest lower Michigan and Northwest Indiana
where the better forcing and moisture will be. Expect 1-2 inches,
with locally higher amounts in locations along/west of US 31.
Otherwise, expect around 1 inch or less further south and east.

The low pressure system taking shape over the plains will lift
northeastward through the period, reaching lower Michigan by about
6z Monday. Stationary boundary associated with this system drapes
from Lake Huron into Illinois by 21z Sunday, which will be the focus for
the precipitation. Think most areas to the southeast will be fairly
dry until Sunday afternoon/evening, once the actual cold front comes
through. It seems like the trend with models is to weaken that front
as it moves eastward, so think the lower rain totals in the
southeast are okay.

Otherwise, winds will be pretty gusty--with hazardous swimming
conditions expected on Lake Michigan. Storm Prediction Center has our area in a marginal
risk for severe weather Sunday afternoon/even given strong llj/waa.
Not out of the question that we could see damaging winds with any
stronger storms-but that being said-mid-level lapse rates are pretty
paltry and think the main threat will be heavy rain. Confidence is
pretty low in severe weather at this point.


Long term...(sunday night through saturday)
issued at 348 PM EDT Sat Sep 21 2019

Conditions dry out once again in the wake of the exiting cold front
Monday morning, continuing into Wednesday morning. Cold air
advection and tightened pressure gradient will lead to a cooler day
on Monday, with breezy northwest winds and diminishing cloud cover.
Temperatures will remain more seasonable, with highs Mon/Tue in the
70s, and lows in the 50s. Expect at least moderate swim risk
conditions on Lake Michigan Monday, with direct onshore wave
directions, wave periods of 5 to 6 seconds, and wave heights of 3 to
5 feet. Winds die down Monday night into Tuesday as surface high
pressure centered over Missouri Monday drifts eastward into southern
Indiana and Kentucky, mitigating any hazards on the lake. By Tuesday
evening the surface high will reach the eastern Seaboard, leaving
our forecast area under a weak upper level ridge through Wednesday

Meanwhile, a surface low pressure system developing over the
Canadian prairie Monday night will shift into northern Ontario by
Tuesday night, then lift northeastward into James Bay/Quebec. Models
disagree with respect to the strength/exact position/speed at which
the low moves, so that will impact our forecast with respect to
precipitation chances/timing/amounts. With this in mind, the
associated cold front will likely move through our County Warning Area from west to
east Wednesday afternoon/evening into Thursday afternoon. Have
associated chances for showers in the forecast, with slight chances
for thunderstorms. High temperatures Wednesday will climb into the
mid-upper 70s. Moderate conditions are possible Wednesday on Lake
Michigan once again, with strong southwest winds ahead of the front
building waves to 3 to 4 feet (especially in Berrien county).

High pressure builds in from the west fairly quick, crossing into
southern Ontario by Friday morning. Models agree at the moment on a
dry forecast for Thursday afternoon and Thursday night, with mainly
morning chances for rain showers in the morning east of I 69
associated with the exiting cold front. Highs will be in the upper
60s and the low to mid 70s (warmest along/south of Highway 24).

Another system will impact our area on Friday, though lower
confidence at this point for higher chance pops. A warm front draped
from southern Indiana to surface low pressure over the Central
Plains will lift northward into our forecast area through Friday
night. Ridge aloft at the time may keep most of our forecast area
dry initially, but some of the guidance suggests warm air advection
will lead to chances for precipitation in the north and west. Will
keep consensus low-end pops for now. Saturday the surface low from
the plains will shift east (or northeast depending on the model),
which increases the chance for precipitation over the area. Kept low
chances given the significant model differences in the placement of
this low. Highs will be in the 70s and low 80s. Lows will be in the


Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 729 PM EDT Sat Sep 21 2019

A few showers or patches of sprinkles were impacting ksbn at the
issuance time, but will quickly shift away. Have maintained vcsh
for anything stray that might pop up, but suspect the bulk of the
activity will remain west and north of the site into the overnight
hours. A few of the models to develop some additional showers
that could impact the site in the 7-11z sun window. Worth watching
with increasing lift across that area, but skeptical based on
current upstream trends. Better chances arrive Sunday afternoon,
but may wait until just outside the period as well.

At kfwa dry VFR conditions look to prevail through the period with
rain finally arriving around or after 21z sun.


Iwx watches/warnings/advisories...
Michigan...Beach hazards statement through Sunday evening for miz077.

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



synopsis...mesoscale discussion
short term...mesoscale discussion
long term...mesoscale discussion

Visit US at www.Weather.Gov/iwx

National Weather Service Glossary of Abbreviations