March 9-11 Severe Weather Potential

The Storm Prediction Center has highlighted portions of the Gulf Coast for a severe weather threat.

SPC

Today's severe weather threat is focused in southeastern Louisiana and extreme southern Mississippi, where a Marginal risk of severe weather has been posted. Radar imagery shows a broad swath of moderate to heavy precipitation across the south-central Plains, feeding on moisture from the Gulf of Mexico. Thunderstorms appear to be moving inland over the Marginal risk area, and it looks as though the main threats will be tornadoes and wind.

SPC

Tomorrow's severe weather threat, for March 10th, is more expansive than today's. We see a Marginal risk of severe weather across eastern Louisiana, southern and central Mississippi, and southwestern Alabama. A general risk of thunderstorms surrounds this more elevated threat delineation. A similar set-up to today should evolve over the central Gulf Coast, as that rich Gulf of Mexico moisture continues to allow for thunderstorms to flow onshore, possibly even training in some spots to lay down heavier totals than forecast.

Andrew

Anomalously Warm Caribbean May Foreshadow Severe Weather Season

The current state of the Caribbean waters into the southern Gulf of Mexico could foretell our upcoming severe weather season.

NOAA

The above image shows sea surface temperature anomalies over the Gulf of Mexico, Caribbean, and southern Atlantic for early March. In this image, we notice a generally average to slightly warmer than average trend for the Caribbean waters, with spots of even warmer waters. Temperatures in the Gulf of Mexico are running above-normal to well-above-normal, particularly south of Louisiana.

As was stated by Storm Prediction Center forecaster Rich Thompson in his Tornado Forecasting Workshop sessions, a more plentiful severe weather season could be in store if you begin with a moist environment down in the Caribbean during the winter months, which can then transfer into the Gulf of Mexico for spring, to provide for a rich moisture source. Going solely by that, we're in a good position for a pre-established moisture source to kick off the severe weather season, best shown by the warm water temperatures from the Gulf Coast straight down to South America. It isn't the warmest water temperature swath we've ever seen, but it's notable.

NOAA

Also an interesting feature is the rock-steady pool of well above-normal water temperatures in the northeast Pacific and Gulf of Alaska. If this can stay in place for the spring season, and we're able to maintain cyclogenesis in the North Pacific to carry storms into North America, it's possible we see a northwest flow-dominated severe weather season, which can feature intense events in the Midwest, Great Lakes, Ohio Valley, and Mid-Atlantic.

I'll have much more on this in my 2015 Severe Weather Season Outlook on Wednesday, March 18th.

To summarize:

- A warm Caribbean and Gulf of Mexico may be setting the stage for at least an average severe weather season.
- SST patterns off the West Coast could also allow for a severe weather focus in the North-Central and Northeast US.
- All of this will be re-evaluated in the severe weather seasonal outlook on March 18.

Andrew 

Long Range Climate Models Forecast El Nino Development in Summer, Fall

After a failed El Nino prediction for this winter, despite the NOAA declaration of the phenomenon in the last few days, model guidance is once again forecasting an El Nino developing in the summer and fall.

JMA

The above image shows the sea surface temperature deviation from normal, centered over the central Equatorial Pacific, forecasted until late 2015. The red line shows observed anomalies to date, while the yellow boxes portray the range of SST anomalies in the forecast period. This particular forecast sees water temperatures warming steadily from late spring into the fall, when the average of the boxes reaches 1.0º C at the very end of the forecast period.

BOM

The next forecast, from the Australian Bureau of Meteorology, shows temperatures quickly warming up from mid-spring onwards, solidly in El Nino territory by the early winter of 2015-2016. This was another model that consistently forecasted an El Nino this past winter, but never verified. It's quite possible we see this happen again this summer and fall.

The atmosphere is, right now, quite conditioned for an El Nino to develop. We have been seeing sustained negative values from the Southern Oscillation Index (SOI), an indicator of El Nino conditions in the atmosphere. This winter, it didn't come out as expected. However, if we keep a similar SST set-up across the Pacific, as well as our pre-conditioned environment for the El Nino, we could see that develop. I remain pretty skeptical, however.

To summarize:

- Model guidance is projecting an El Nino to form for the summer and fall months.
- Because the majority of model guidance was incorrect in their forecasts this past winter, uncertainty is extremely high.

Andrew

Long Range Outlook for March, Early April 2015

This is the Long Range Outlook for the period of March 2015 into early April 2015.

Paul Roundy

The above image is pretty complicated, but bear with me and it won't be so bad. This chart shows a longitude-by-time forecast for tropical convection anomalies (colored shadings) between 7.5º North and 7.5º South latitude, centered on the Equator. Blue colors correspond to enhanced tropical convection (thunderstorms), while yellows are indicative of suppressed convection. There are a lot of lines here, but the only ones we need to worry about are the red lines, which show the active phase of the Madden-Julian Oscillation in solid (dashed is the suppressed 'phase'), as well as the Kelvin Wave, which is in thin pink.

We currently see an MJO wave evolving from about 75 degrees East, as the red lines in that longitudinal sector show. It is expected that this wave will strengthen in the next week or two as an Equatorial Rossby Wave moves over the region, shown as a light-green delineation. The placement of tropical convection in this part of the world is equivalent to a Phase 4 MJO event. As shown in the image below, temperatures during a Phase 4 event will tend to lean warmer than normal for much of the country, but a deep snowpack across much of the North and Central parts of the US tells me this warm-up could very well be muted around March 12th.

CPC

A Kelvin Wave then forms around that March 12th period, and this convectively-coupled Kelvin Wave traverses the Pacific in time for the final days of the month. This very progressive tropical forcing theme tells me the country is likely in for some roller coaster weather patterns for the remainder of the month, despite the MJO wave signal only shifting eastward slowly in contrast to the Kelvin Wave movement. This particular chart has us reaching Phase 5 of the Madden-Julian Oscillation by the final days of March, which would typically favor a cooler than normal pattern for the Northern US.

However, this cold outlook for the end of March is working in contrast to a projected pattern shift in the Pacific, in which ensemble guidance sees a trough positioning itself along the west coast of North America to permit warmer weather in the Central and East US. With warm signals coming from the Typhoon Rule as Japan undergoes a generally-warm pattern in the next two weeks-plus, and tropical forcing not really being effective this past month due to such dominance from the Pacific pattern, I'll opt for a warmer outlook to close March.

To summarize:

- An overall cool pattern should remain in place through about mid-March.
- Model guidance is then indicating, at the very least, the synoptic (overall) weather pattern will undergo some changes for the last half of March. I see this as being a good shot for a warmer pattern.
- This warmer pattern could continue into early April.

Andrew

March 4-5 Potential Ice Storm

There is an increasing likelihood that accumulating ice will pose a threat to residents in the Southern US.

PSU

High resolution precipitation-type forecasts show rain impacting the states of Mississippi, Georgia, and Alabama into the Carolinas late on March 4th into the 5th, before widespread icing begins to take hold. Areas affected include northern Mississippi, northern Alabama, central Tennessee, eastern Kentucky, and portions of the Mid-Atlantic. Snowfall may then be expected to the north.

WxCaster

Ice accumulations from the GFS model lay down pockets of close to 0.50" in portions of Arkansas and Tennessee, as well as Texas and Louisiana. Model guidance usually doesn't do well with freezing rain forecasts, but amounts over 0.10" are very possible, if not likely, in northern Mississippi into Tennessee.

To summarize:

- An ice storm may impact the South US on March 4th and 5th.
- Accumulations could reach as high as 0.25" of ice in many areas, with isolated higher amounts.

Andrew