Area Forecast Discussion
Issued by NWS Goodland, KS

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FXUS63 KGLD 240535
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
1135 PM MDT Mon Apr 23 2018

.UPDATE...
Issued at 915 PM MDT Mon Apr 23 2018

Main change was to increase PoPs and QPF based on the trend of
near term data. Looks like the rainfall will be moving through in
two waves, the first wave is beginning to move in from the west.
The frontogenesis is not as strong as with the second round, so
the storm coverage will not be all that high. In addition the lift
from this first upper level short wave trough seems to outpace
the slower saturating environment and frontogenesis, causing the
storms to end as they move east through the night. However, as
this first wave begins to diminish around sunrise, the second
wave of rainfall begins to form as another upper level short wave
trough develops upstream of the first one. The saturated
environment and frontogenesis move much further east with this
second wave. The higher amounts of rainfall will be where the
storms from the second wave can train over the same area. The
rainfall will end from west to east Tuesday afternoon and
evening.

Latest near term data shows the QPF higher than the forecast and
most synoptic scale models runs. Based on the training nature of
the storms during the morning, this seems reasonable. The high end
of the near term data ensemble suggests the north half of the
forecast area could receive an inch of rainfall. However this
seems high considering the rainfall is coming through in two
waves instead of one slow moving wide spread rain event. The mean
rainfall amount is between a quarter and half an inch, much more
reasonable given the environment. Therefore have increased
rainfall amounts for tonight and tomorrow.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 257 PM MDT Mon Apr 23 2018

Main forecast concerns will be frontal passage tonight and
chance/phase of precipitation across the area through Tuesday.
At jet level...looked to start out fine. At mid levels...models were
pretty close with the Ecmwf and Canadian starting out the best.
Models were not too far apart on the low level thermal field with
the Nam doing a little better.

Strong cold approaching from the northwest. Currently over eastern
Wyoming. This front push into the western portion of the area in the
mid and late evening hours and through most of the area by late
tonight and south of the area by mid morning. Gradient and pressure
rises support windy conditions behind this front.

Left front quadrant moves across the area during the morning. By
late afternoon, the jet axis lies across the northern portion of the
area. Potent and compact upper is moving into Wyoming from Montana
at this time. This system still to the north and west of the area
late tonight and will push across the area during the day tomorrow.

Lift will begin with the front and then increase through the night.
The brunt of the mid and upper forcing will occur later tonight and
through morning tomorrow. Very strong baroclinic and mesocale
forcing to move across through this period. Progression of pops and
storm has slowed up a little. Elevated cape near zero to negative
theta-e lapse rates will be in place through the night. As a result
added isolated thunderstorms to the precipitation through the night.

For the phase, I ended up keeping it rain. However, it will be close
to becoming mixed in the far western portion late tonight and early
tomorrow morning. Theta-e lapse rates are a little higher with no
elevated Cape around. Will the showery mention through the day.
Because of the thick cloud cover through the day ongoing
precipitation and cold air advection, lowered high temperatures from
the previous forecast.

.LONG TERM...(Tuesday night through Monday)
Issued at 240 PM MDT Mon Apr 23 2018

H5 low pushes southeastward Tuesday night into Wednesday morning
with showers winding down from west to east. Lingering showers will
remain in the eastern portions of the area through mid morning.
Colder air will be ushered in from the north as we approach sunrise
on Wednesday, giving us cooler than average low temperatures across
the CWA.

Shortwave high pressure prevails from late Wednesday through Friday
with dry weather and warmer temperatures each day. H5 low pressure
approaches the region late Friday into Saturday as the ridge
retreats eastward. Surface flow turns southerly, allowing a long
fetch of moisture to advect into the region. CAPE values increase
significantly by midday Saturday using the GFS as guidance; however,
there is not much in the way of agreement between the global models
and thus confidence is low in this solution. If models come into
better agreement, I will have better confidence in the possibility
of thunderstorm development along a theta-e boundary Saturday
afternoon/evening. If this occurs, severe storms are possible,
especially along and west of HWY 25.

Confidence remains low going into Sunday, as the GFS develops
potentially severe thunderstorms along a theta-e/frontal boundary
Sunday afternoon. The ECMWF holds onto the ridge a bit longer, thus
inhibiting thunderstorm development.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1130 PM MDT Mon Apr 23 2018

VFR to IFR conditions forecast for the TAFs. Cold front is moving
into NWKS from the northwest. Along the front showers/t-storms
have developed. Am expecting the storms to decline in coverage or
atleast not expand in coverage, until around 9z or so. Once the
front moves through the ceiling will fall to MVFR, possibly as low
as IFR for KGLD. Confidence in IFR ceiling occurring at KGLD has
increased based on model data, but am expecting it to be short-
lived and only along/just behind the front.

NW winds will be breezy during the morning behind the front then
gradually decline in the afternoon. Meanwhile the ceiling will
gradually raise during the afternoon as the rain ends from west to
east.

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

$$

UPDATE...JTL
SHORT TERM...BULLER
LONG TERM...TL
AVIATION...JTL



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