April 17-30, 2005 Pattern Discussion

[donsutherland1]

Last week’s discussion raised a number of issues of what one might expect for the April 10-23, 2005 period.

• In the Northeast and Mid-Atlantic region, a strong cold front will likely arrive on Monday, April 11 with perhaps some showers. Some of those showers could end as snow showers across parts of central and upstate New York and central and northern New England. There is a slight chance that some of the frozen precipitation might make it into the Boston area. The morning of April 12 should be unseasonably cold. Boston and possibly New York City could see readings fall below 30°. Philadelphia should see a low temperature in the low 30s.

A strong cold front moved across the Northeast and Mid-Atlantic on April 11. April 12 saw a trace of snow in Boston. April 12 low temperatures, though, were much higher than the idea noted above:

Boston: 33°
New York City: 37°
Philadelphia: 38°

• By April 13, a slow warming trend should commence. During the April 16-17 period, the warmup could accelerate. The April 18-23 timeframe looks to be unseasonably warm and generally dry. Temperatures could again reach into the 70s as far north as southern New England on one or more days. 80° or above is possible on one or more days in Washington, DC and Philadelphia.

April 14 was a warmer day with readings rising well into the 60s from New York City southward. April 15 saw readings return back to the 50s. However, computer guidance strongly indicated much warmer readings during the weekend and first half of next week.

• Ahead of the strong cold front that will affect the East, temperatures in the Central Plains could spike to much above normal levels on April 10. Detroit will likely see readings close to 70° and Chicago should make it into the 70s.

April 10 high temperatures:
Chicago: 79°
Detroit: 76°

• The evening of April 10 into April 11 could see some rain followed by cooler but not cold readings. April 15 should mark the beginning of a warmup that will likely see above normal readings during the April 18-23 timeframe.

A trace of rain in Chicago but Detroit saw no rain on April 11. Noticeably cooler weather arrived in both cities with highs at 54° in both Chicago and Detroit on April 12. Highs in both cities were in the lower 60s on April 15.

• In the Central Plains, temperatures will likely run above normal through April 10. Both Omaha and Kansas City could see readings reach or exceed 70°.

April 10 highs:
Kansas City: 79°
Omaha: 75°

• The April 11-13 period could see rainfall and somewhat cooler readings at Kansas City, with the wet period beginning about a day earlier in Omaha.

April 11 rainfall:
Kansas City: 0.57”
Omaha: 0.75”

The April 12 high was 52° in Kansas City and 49° in Omaha.

• April 15 could see the arrival of much above normal readings.

Temperatures peaked in the lower 70s in Kansas City and Omaha on April 15.

• The dry start in eastern Texas should end. April 10-11 and then April 15-16 could see significant rainfall of 0.50” or more.

April 11 rainfall in Houston came to 0.88”. Computer guidance suggested no rainfall for April 15-16.

• The April 10-15 period will likely be cooler than normal with frequent showers in Seattle. April 10-11 could see more than 0.25” rain.

The April 10-14 timeframe saw Seattle’s temperature average 4.5° below normal. April 10-11 rainfall totaled 0.68”.

• April 13-14 could see some unseasonably cold readings with perhaps lows falling to or below 35° on at least one day.

The coolest day of the cool spell through April 14 was April 12 with a low temperature of 36°.

• After a cool weekend in Los Angeles, temperatures should again rise. April 11-16 should see above normal readings. Toward the end of that period, it is possible that mercury will break 80°. Very little if any precipitation is likely through April 16.

The weekend (April 9-10) saw the temperature average 2.5° below normal in downtown Los Angeles. Afterward, the temperature (April 11-14) came out 0.75° above normal. Monthly rainfall through April 14 was a Trace.

The April 17-30, 2005 Ideas:

Through the first half of this period, genuine springlike warmth will likely prevail in the eastern United States. Temperatures could feel summerlike on at least one or two days. The latter part of the second half of the period could see significantly cooler air in the East.

• The April 17-22 period will likely see temperatures average much above normal in the Northeast and Mid-Atlantic regions. During this period, the highest temperature could reach close to 78° in New York City, the lower 70s in Boston, and 83° or above in Washington, DC. A cool front could bring some showers later in the week (April 21). Afterward a short cool period, readings could again warm during the weekend (April 23-24). The following week could see a noticeably colder air mass. The potential exists for low temperatures to fall to 43° or below in Boston, 45° or below in NYC, and 47° or below in Washington, DC on one or more days during the April 25-May 5 timeframe.

• The April 17-20 period will likely see readings in the Chicago and Detroit areas average much above normal. The warmest days will likely be April 19-20. Temperatures could soar to 75° or above in both Chicago and Detroit on one or both days. Rain is possible late on April 20 into April 21. Much cooler readings should follow. Moderation is likely to commence during the weekend. An even colder air mass could arrive early the following week (April 25-26).

• The April 17-20 period will likely feature much above normal readings in the Central Plains states. Temperatures could reach 75° or above on two or more days during this timeframe. A soaking rain is possible on April 20. Cooler weather should follow in the wake of the storm. A fresh warmup could commence during the weekend.

• In Seattle, the April 17-19 period will see below normal temperatures and some rainfall. By April 21, it temperatures should be running above normal. A drier and milder pattern could be sustained after April 25.

• Temperatures in Los Angeles should run somewhat above normal through April 18. Somewhat cooler air could affect the city during the April 19-20 timeframe. Warmth should gradually begin to build on April 21.

Will there be an El Niño during the Summer?

With the rise in the MEI that continued through the February-March period, with the February-March figure ranking 7th highest for that point in time, the question as to whether there will be an El Niño present during the upcoming hurricane season arises.

In the 10 years in which the MEI was most similar to the 2004-05 one over the past 6 months, 7 of those 10 (70%) years saw neutral ENSO conditions. 3/10 (30%) saw El Niño ones. In the 15 most similar matches, 10/15 (67%) saw neutral ENSO conditions. The remaining 33% saw an El Niño. From this pool of 15 seasons, 4/6 (67%) that saw the February-March MEI range from +0.500 to +1.500 experienced neutral ENSO conditions. The remainder saw a summer El Niño.

Major Caveat: The most similar season with regard to the MEI was 1992-1993. The average difference from the 2004-05 figure was 0.160. Summer 1993 saw the weak winter El Niño blossom into a moderate one during the spring and summer months. 1993 had 8 named storms.

An examination of ENSO region anomalies, finds an identical profile. 7 of the 10 (70%) closest matches saw neutral ENSO conditions during the summer. 3/10 (30%) saw El Niño conditions. 10/15 (67%) saw neutral ENSO conditions and 5/15 (33%) experienced El Niño conditions.

The March 2005 ENSO forecast saw 10/16 (63%) models below El Niño threshold for June-August. Through September-November, 9/17 (53%) remained below El Niño threshold. In sum, it appears unlikely that there will be El Niño conditions during the heart of the summer (June-August).

NOTE: After April, this discussion will appear only in the U.S. Weather Watch Forum until next fall.

[W13]

Great discussion as always, Don.

[donsutherland1]

In the above discussion, with strong reliance on a signal in the GFS ensembles, I had noted: The following week could see a noticeably colder air mass. The potential exists for low temperatures to fall to 43° or below in Boston, 45° or below in NYC, and 47° or below in Washington, DC on one or more days during the April 25-May 5 timeframe.

April 25 Minimum Temperatures:
Boston: 41°
New York City: 40°
Washington, DC: 40°