506
FXUS06 KWBC 091916
PMDMRD
Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks
NWS Climate Prediction Center College Park, MD
300 PM EDT Thu May 09 2024

6-10 DAY OUTLOOK FOR MAY 15 - 19 2024

Today`s dynamical model solutions are in fairly good agreement on the predicted
500-hPa circulation pattern across North America and surrounding regions during
the 6-10 day period, and are quite similar to yesterday. Yesterday, the
operational GFS and ECMWF models showed a more amplified 500-hPa height pattern
than the ensemble means, but these have shifted toward the less-amplified
ensemble means today, supporting this solution. The ECMWF and Canadian ensemble
means are very similar, featuring a strong anomalous mid-level mean ridge
southwest of Alaska, subnormal 500-hPa heights across Alaska and adjacent
Canada, positive mid-level height anomalies in the Pacific Northwest extending
into the northern Rockies, near- to slightly below-normal 500-hPa heights in
the eastern CONUS, and a downstream mid-level ridge east of Atlantic Canada.
The only substantial difference across the CONUS is that the Canadian ensemble
mean keeps slightly higher mean 500-hPa heights in the South Atlantic region,
but this has little effect on sensible weather. The GEFS ensemble mean is
slightly different, featuring less mid-level troughing across southern Alaska,
less anomalous ridging in the Pacific Northwest, and slightly greater 500-hPa
heights in the Southwest, and a moderate anomalous mid-level ridge centered
near northeastern Canada. The pattern shown by the ECMWF ensemble mean is
favored given slightly better agreement with its solution than yesterday, but
all three show a relatively flat pattern with weak mid-level features affecting
Alaska, Hawaii, and the CONUS.

GEFS and European ensemble mean raw, bias-corrected, calibrated, and reforecast
temperatures all favor above-normal temperatures for most or all of the CONUS,
with the weakest odds in portions of the Lower Mississippi Valley and interior
Southeast. Here, slightly below-normal 500-hPa heights and moderate to heavy
rainfall on the cooler side of a quasi-stationary front could serve to keep
temperatures closer to normal. The highest probabilities favoring above-normal
temperatures exceed 70% over southern Florida, with odds topping 60% over the
entire Florida Peninsula, the Great Basin and adjacent areas, and locations
near and west of the Appalachians in the Northeast, all similar to the
consolidation. 500-hPa mean heights near Hawaii are forecast to be near or
slightly below normal by all ensemble means, with weak anomalous mid-level
ridging to the west and the east, leaving the island chain in an area with no
marked shift of the odds toward either above- or below-normal temperatures.
Farther north, despite decent model agreement, dynamic model temperatures and
especially the derived tools were in conflict across Alaska. Analogs were cold
throughout the state. The consolidation shows cold weather favored in
southeastern and southwestern parts of the state, with warmer than normal
weather favored closer to the Arctic Circle. The reforecasts were sharply
different, with the GEFS showing subnormal temperatures dominating almost the
entire state while the ECMWF reforecast confines enhanced chances for
below-normal temperatures to part of southwestern Alaska, with increased odds
for above-normal temperatures over the northern half of the state. The official
forecast is a compromise of the tools, with increased odds for colder than
normal weather across the southern half of the state and no tilt of the odds
indicated farther north.

Below-normal precipitation is favored from the interior western CONUS (outside
climatologically dry areas), with no tilt of the odds toward wetness or dryness
closer to the Pacific Coast. This is supported by GEFS and ECMWF reforecast
precipitation, as well as the raw ECMWF ensemble mean output. For most of the
remainder of the CONUS, these two reforecasts depict increased odds of
above-normal precipitation, which is consistent with broad, low-amplitude
cyclonic flow. The highest probabilities for above-normal precipitation, in
excess of 60%, are indicated over the central Gulf Coast region. This is
associated with increased onshore flow from the Gulf Coast states interacting
with a quasi-stationary front in a region of weak mid-level troughing. The
ECMWF ensemble mean depicts more than 2 inches of rain during the period over
portions of the central Gulf Coast region while the GEFS mean, in the same
location, keeps the totals closer to 1.5 inches. The consolidated tercile
probabilities show the greatest odds of above-normal rainfall in this region as
well. In Alaska, above-normal precipitation is weakly favored over most of the
state associated with broad mid-level troughing. Similarly, slightly enhanced
chances for above-normal precipitation cover Hawaii the proximity of weak
500-hPa troughing.


The official 6-10 day 500-hPa height blend consists of 20% of Today`s 0z GFS
Ensemble Mean centered on Day 8, 30% of Today`s 0z European Ensemble Mean
centered on Day 8, 20% of Today`s operational 0z ECMWF centered on Day 8, and
30% of Today`s 0z Canadian Ensemble Mean centered on Day 8


FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Above average, 4 out of 5, due to
good agreement among model solutions and forecast temperature and precipitation
tools in most areas.

8-14 DAY OUTLOOK FOR MAY 17 - 23 2024

The ensemble means start to diverge during the 8- to 14-day period,
particularly across the western CONUS. All models keep slightly below-normal
500-hPa heights from the Upper Mississippi Valley through most of the eastern
CONUS, but differences begin to evolve farther west. The Canadian and ECMWF
ensemble means increase 500-hPa heights in the western CONUS, leading to a weak
but distinct anomalous 500-hPa ridge over much of western North America. The
GEFS, on the other hand, lowers mid-level heights in the Pacific Northwest and
keeps any weak anomalous ridge development flat and confined to the Southwest.
The manual blend favors the weak anomalous ridge covering the western CONUS as
it is more consistent with the 6- to 10-day 500-hPa mean pattern, and is
depicted by a preponderance of model solutions, but with low confidence given
the low amplitude of the pattern and the weakness of individual mid-level
features. Farther west, the moderately strong 500-hPa ridge southwest of Alaska
is expected to remain essentially unchanged during week-2 while mid-level
heights across Alaska slowly climb toward normal, slightly more markedly in the
ECMWF ensemble mean than the Canadian ensemble mean or the GEFS mean. A weak
trough and near-normal 500-hPa heights are predicted in the vicinity of Hawaii,
although the placement and magnitude of features are not consistent among the
models.

With the official forecasts leaning with low confidence toward a solution
featuring a fairly well-defined mid-level ridge in the western CONUS with a
weak trough to the east, there is more uncertainty in the temperature pattern
from the Plains eastward, and in much of this region, the forecast shows no
tilt of the odds favoring either unusually warm nor unusually cool weather.
Farther west, the weak mid-level ridge favors above-normal temperatures, with
the best odds across the interior West and Southwest where there is better
model agreement on positive 500-hPa height anomalies. Across Alaska, the tools
differ significantly on temperatures, as during the 6- to 10-day period. Each
individual tool, however, is at least slightly warmer during week-2 than it is
for days 6-10, and the official forecast has followed this scenario. Odds for
below-normal temperatures are less enhanced and confined farther to the south
while slightly enhanced chances for above-normal temperatures extend across
portions of northern Mainland Alaska. 500-hPa heights increase slightly across
Hawaii during week-2, but remain close to normal in a pattern slightly favoring
above-normal temperatures over the western half of the state.

The uncertainty in the evolving 500-hPa pattern is reflected in the week-2
precipitation outlook. Across most of the western half of the CONUS, the
official forecast shows equal chances of all precipitation terciles, save for
below-normal precipitation slightly favored in the southern Rockies and High
Plains, where there is slightly better model consensus that the region will be
downstream from anomalously high 500-hPa heights. Farther east, the lower than
normal mid-level heights marginally favor above-normal precipitation in most
locations, with better odds over the Southeast, where the GEFS mean drops 1.5
to 2.5 inches of rain during the period. The ECMWF ensemble shows significant
odds for a deepening trough to bring heavy rainfall farther north later in the
period, toward New England, but none of the other tools are as amplified at
this time, and for now this solution is not preferred. The weak mid-level flow
pattern across Alaska slightly elevates the chances for above-normal
precipitation statewide, and in Hawaii, the proximity of a surface frontal
system marginally enhances the odds for surplus precipitation in the western
islands, but prevailing surface high pressure may serve to slightly reduce
precipitation totals across the Big Island.

The official 8-14 day 500-hPa height blend consists of: 30% of Today`s 0z GFS
Ensemble Mean centered on Day 11, 35% of Today`s 0z European Ensemble Mean
centered on Day 11, and 35% of Today`s 0z Canadian Ensemble Mean centered on
Day 11


FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Below average, 2 out of 5, with
model disagreement on the overall circulation pattern increasing with time, and
weaker signals in the precipitation and temperature tools.

FORECASTER: Rich Tinker

Notes:


Automated forecasts are issued on Saturday and Sunday. Occasionally manual
intervention is necessary to address quality control and consistency issues. In
these cases, forecasts are manually drawn but a full discussion is not issued.


The notation for the categorical forecast indicated on the maps is the same as
that in the tables: A-above   N-near normal   B-below


The temperature map shows regions with > 33% chance of being warmer (orange,
"A"), colder (blue, "B"), or close to (unshaded, "N"). Historical average
values for the calendar period of the forecast (dashes, "f").  Labels on the
shaded lines give the probability (> 33%) of the more likely category (B or A).
 Probability of N is always < 40%.


The precipitation map shows regions with > 33% chance of being wetter (green,
"A"), drier (tan, "B"), or close to (unshaded, "n"). Historical median values
for the calendar period of the forecast (dashes, "inches").  Labels on the
shaded lines give the probability (> 33%) of the more likely category (B or A).
 Probability of N is always < 40%.


In the southwest and other climatologically dry regions - there will be a
greater than 33.3% chance of no precipitation and occasionally even a normal
(i.e. Median) value of zero - especially during the dry seasons.  In such cases
a forecast of near normal is effectively a forecast of little or no
precipitation.


The climate prediction center uses 1991-2020 base period means as reference in
the climate outlooks.

The next set of long-lead monthly and seasonal outlooks will be released on May
16.


Analogs to the 5 day mean observed pattern centered 3 days ago (D-3)
for the region from 20N to 70N latitude and 175E to 60W longitude
include the 5 day periods centered on the following dates:
19750427 - 19760424 - 19750502 - 19850513 - 19650507


Analogs to the 7 day mean observed pattern centered 4 days ago (D-4)
for the region from 20N to 70N latitude and 175E to 60W longitude
include the 7 day periods centered on the following dates:
19750428 - 19760424 - 19820518 - 20060505 - 19750503


6-10 DAY OUTLOOK TABLE
Outlook for May 15 - 19 2024

STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN
WASHINGTON  N    N     OREGON      A    B     NRN CALIF   A    N
SRN CALIF   A    N     IDAHO       A    B     NEVADA      A    B
W MONTANA   A    B     E MONTANA   A    N     WYOMING     A    N
UTAH        A    B     ARIZONA     A    N     COLORADO    A    A
NEW MEXICO  A    A     N DAKOTA    A    A     S DAKOTA    A    N
NEBRASKA    A    N     KANSAS      A    A     OKLAHOMA    A    A
N TEXAS     A    A     S TEXAS     A    A     W TEXAS     A    A
MINNESOTA   A    A     IOWA        A    A     MISSOURI    A    A
ARKANSAS    A    A     LOUISIANA   A    A     WISCONSIN   A    A
ILLINOIS    A    A     MISSISSIPPI A    A     MICHIGAN    A    A
INDIANA     A    A     OHIO        A    A     KENTUCKY    A    A
TENNESSEE   A    A     ALABAMA     A    A     NEW YORK    A    A
VERMONT     A    A     NEW HAMP    A    A     MAINE       A    A
MASS        A    A     CONN        A    A     RHODE IS    A    A
PENN        A    A     NEW JERSEY  A    A     W VIRGINIA  A    A
MARYLAND    A    A     DELAWARE    A    A     VIRGINIA    A    A
N CAROLINA  A    A     S CAROLINA  A    A     GEORGIA     A    A
FL PNHDL    A    A     FL PENIN    A    A     AK N SLOPE  N    A
AK ALEUTIAN B    N     AK WESTERN  B    A     AK INT BSN  N    A
AK S INT    B    A     AK SO COAST B    A     AK PNHDL    B    A



8-14 DAY OUTLOOK TABLE
Outlook for May 17 - 23 2024

STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN
WASHINGTON  A    N     OREGON      A    N     NRN CALIF   A    N
SRN CALIF   A    N     IDAHO       A    N     NEVADA      A    N
W MONTANA   A    N     E MONTANA   A    N     WYOMING     A    N
UTAH        A    N     ARIZONA     A    N     COLORADO    A    N
NEW MEXICO  A    N     N DAKOTA    N    N     S DAKOTA    N    N
NEBRASKA    N    A     KANSAS      A    N     OKLAHOMA    A    N
N TEXAS     A    N     S TEXAS     A    B     W TEXAS     A    B
MINNESOTA   N    N     IOWA        N    A     MISSOURI    N    A
ARKANSAS    N    A     LOUISIANA   A    A     WISCONSIN   N    N
ILLINOIS    N    A     MISSISSIPPI N    A     MICHIGAN    N    A
INDIANA     N    A     OHIO        N    A     KENTUCKY    N    A
TENNESSEE   N    A     ALABAMA     N    A     NEW YORK    N    A
VERMONT     N    A     NEW HAMP    N    A     MAINE       A    A
MASS        N    A     CONN        N    A     RHODE IS    N    A
PENN        N    A     NEW JERSEY  N    A     W VIRGINIA  N    A
MARYLAND    N    A     DELAWARE    N    A     VIRGINIA    N    A
N CAROLINA  A    A     S CAROLINA  N    A     GEORGIA     N    A
FL PNHDL    A    A     FL PENIN    A    A     AK N SLOPE  N    N
AK ALEUTIAN B    B     AK WESTERN  B    N     AK INT BSN  N    N
AK S INT    B    N     AK SO COAST B    N     AK PNHDL    B    N

                           LEGEND
TEMPS WITH RESPECT TO NORMAL     PCPN WITH RESPECT TO MEDIAN
A - ABOVE   N  - NEAR NORMAL     A - ABOVE   N - NEAR MEDIAN
B - BELOW                        B - BELOW

THE FORECAST CLASSES REPRESENT AVERAGES FOR EACH STATE. NORMAL
VALUES - WHICH MAY VARY WIDELY ACROSS SOME STATES - ARE
AVAILABLE FROM YOUR LOCAL WEATHER SERVICE FORECAST OFFICE.

FOR ADDITIONAL INFORMATION SEE MESSAGE FXUS06 KWBC - ON AWIPS AS
PMDMRD.

$$