*Blog written May 12, 2013*
Thus far in 2013, it has been a pretty inactive severe storm season. Blocking patterns over the Pacific and western CONUS are the primary reasons why it has been relatively quiet. It also didn’t help that unseasonably strong cold fronts swept through the Plains as recent as the first week of May. I believe those types of cold fronts are over, until the fall of 2013. However, the atmosphere is already showing signs of transitioning into a summer-like pattern. So much for spring! All hope isn’t lost, though, at least not yet.
May 12 – 14
Sunday looks to be fairly quiet around the lower 48. An mid-level low, located over the Great Lakes region will be progressing eastward along the US/Canada border, and eventually northeast by the start of the week, next week. The associated cold front, at the surface will be moving southeast across the state of Florida. Thus, this will likely be the area (along the cold front) with the best opportunity to see severe weather on Sunday, May 12.
On Monday, May 13, a pretty significant shortwave trough will be entering the Pacific Northwest. This will create height falls downstream of the trough, in the states of Idaho and Montana. With bulk shear values of 50-60 knots from the SW, dewpoints in the 40s and 50s, and strong dynamical lift, organized severe weather is likely for Montana and Idaho, and possibly on the eastern edges of Washington and Oregon. As far as the rest of the country, a strong ridge will be in place over the southwest US and northwest Mexico. This means mainly dry weather for much of the southwest and central CONUS. The mid-level low, mentioned on Sunday, will be too cold to support severe weather in the northeast. In fact, it might be cold enough to snow in the northeast.
Severe weather on Tuesday, May 14, will depend on what the shortwave trough (from Monday) will do in the Northern Plains. GFS and ECMWF disagree with the outcome of the shortwave. The ECMWF lifts it into Canada late Monday night, while the 00z GFS has a closed low forming and trekking along the US/Canada border. Given enough moisture in the lower levels, this could give some support for severe weather for North Dakota and Minnesota, if the trough doesn’t lift too far north.
May 15 – 19
A lot of assumptions are made with any forecast after 3 days out. On Wednesday, May 15, a weak mid-level low/trough will be lifting northeast out of northwest Mexico and into the Southern Plains. GFS and NAM are a little faster than the ECMWF with this feature. All of the models agree, however, that there will be little shear to work with. Therefore, severe storms will be isolated (if they occur) across Texas and Oklahoma, and possibly into Kansas. Surface dewpoints will not be a problem. Lower and mid-60s dewpoints will be spread out across the Southern Plains by Wednesday afternoon.
The weak shortwave trough will be lifting into the Midwest and Mississippi Valley by Thursday, May 16. This will likely spark showers and thunderstorms from eastern Oklahoma to southern Indiana. Some of these storms may become severe, though there are still questions about how these storms will be organized. Nonetheless, hail and wind will be the main threats across these areas. A severe outbreak is not likely, but things can change between now and then.
Friday (May 17) and Saturday (May 18) will have to closely monitored over the next few days. A moderately amplified, open, trough will be digging into the central CONUS by Friday. Forecast models are also hinting at lee-cyclogenesis, or a developing surface low on the lee side of the Rocky Mountains. It’s hard to say exactly where this low will form and where it will track after it forms. Strong mid and upper level lift, along with strong bulk shear, and ample low level moisture will support for organized severe weather on both days. Models are hinting at dewpoint temperatures in the mid 60s and even lower 70s in places. I can’t really tell you much, since it is almost a week out of range, but I can tell you that severe weather will likely somewhere in the Plains (from South Dakota to Texas) on both of these days. I hope to get another blog going before then.