####018009025#### FGUS71 KGYX 281524 ESFGYX MEC001-005-007-011-013-015-017-023-025-027-031-NHC001-003-005-007- 009-011-013-015-017-019-291530- Winter/Spring Flood Potential Outlook National Weather Service Gray ME 1124 AM EDT Thu Mar 28 2024 ...SPRING FLOOD POTENTIAL OUTLOOK FOR NEW HAMPSHIRE AND WESTERN MAINE... The flood potential outlook for New Hampshire and Western Maine is above normal. This is the seventh in a series of regularly scheduled flood potential outlooks that are issued during the winter and spring seasons highlighting the flood potential during the next two-week period. This issuance represents the flood risk between March 28 through April 11 for New Hampshire and western Maine. ...OBSERVED SNOW DEPTH AND WATER EQUIVALENT… The snow depth and snow water equivalents were below normal for all areas apart from the White Mountains where snowpack was near normal. The two-week change in snow conditions was notable growth due to a significant storm on March 23. This single event brought widespread 1.75 to 2.75 inches of additional snow water equivalent to most of the region. The event was complex with snow, rain, sleet, and freezing rain. For the mountains and foothills new snowfall was 1 to 2 feet deep, lesser to the coast where ice played a more significant role. The rainfall event ongoing at the time of this issuance was ripening the snowpack with the expectation that there would be a notable reduction in depth, both from compaction and melt. Far southeastern sections of New Hampshire reported bare ground. Across the remainder of southern New Hampshire...snow depths were mostly under 6 inches now with up to a foot above about 1000 feet. Across central and northern New Hampshire...snow depths averaged 6 to 12 inches in the valleys but do increase to between 1 and 3 feet above 2000 feet with isolated higher depths near treeline in the White Mountains. For example...43 inches of snow was observed on the ground on 27 March at Carter Notch at an elevation of 3317 feet. Snow depths were near normal across portions of southern and central New Hampshire for the end of March but were generally below normal across northern Coos County near the Canadian border. Across southern New Hampshire...between a Trace and 2 inches of water was available for melt runoff with higher amounts limited to areas above 1000 feet. Across the remainder of central and northern New Hampshire...1 to 4 inches of water was held in the lower elevation snowpack but those amounts do increase to between 4 and 8 inches above 1500 feet with even higher amounts in the highest elevations of the White Mountains. As of 26 March 2024...Moose Falls...near the border with Quebec Province Canada...reported 8.6 inches of water in the 30 inch snowpack. And at 4373 feet in the White Mountains...Gray Knob reported more than a foot of water in the 49 inch snowpack. Snow water equivalents have recovered to near normal across a lot of central and northern New Hampshire, but remain a bit below normal across southern portions of the Granite State. In Western Maine the snowpack had rebounded with the recent snow event, but depths remained generally below normal. From the Mountains to the Canadian Border the snow was more continuous and ranged from 1 to 2 feet deep, highest above 2000 feet. Some of the higher peaks in western Maine had over half a foot of water in the high elevation snowpack. The stored water ranged from 3 to 6 inches with locally higher amounts. The foothills ranged from 1 to 2 inches of stored water with depths around 6 to 10 inches. The ice storm along the coast had depths of only a few inches, but stored water averaging around an inch. The snow condition was compressed with high densities. The ongoing rain on snow event was causing melt and ripening even in the mountains with densities around 30% or higher. The snow temperatures were warming and primed to melt over the next two weeks. Looking ahead the forecasts favors gradual melt with the potential for additional snow the first week in April. Thereafter there will be limited opportunities for growth. ...SOIL MOISTURE AND WATER SUPPLY CONDITIONS... After what was an abnormally dry February...the return to excessive wetness for most in March combined with snowmelt dramatically increased moisture states. Much of southern and Western Maine had thawed prior to the recent snowfall event including in the Rangeley area. Frost depths were reduced in mid March with most lower elevations thawing. In the mountains depths ranged from 5 inches in the mountains to 12 inches across the region. The groundwater remained well above normal with additional recharge over the last few weeks as thawing increased. Streamflow levels courtesy of the USGS were running above to well above normal due to a recent rain on snow event. Runoff storage capacity remained well below normal for the time of year with high lake levels for most of the region. Water supply reservoirs across the region continue to average above to much above normal pool levels. Kennebec River Basin storage was 80 percent full as of 25 March 2024 which was 123.2 percent above normal. The nearby Androscoggin River storage was 70.7 percent full which was 128.8 percent above normal. Storage remains high in the Connecticut and Merrimack watersheds where USACE reservoirs had only used 0-3% capacity. Lake Winnipesaukee...New Hampshire's largest lake…showed 0.5 feet above normal levels with continued drawdowns ongoing. ...RIVER AND ICE CONDITIONS... The ice threat has ended for the season. …CLIMATOLOGY AND TEMPERATURE AND PRECIPITATION OUTLOOKS… Temperature and precipitation in March continued the theme over the winter of being above normal. Precipitation for the month to date was running in the top 5 wettest, with Portland and Augusta approaching the record. The month started off with above normal temperatures, but in the mountains conditions still supported snowpack growth. By the last week temperatures dropped below normal allowing a significant snowfall event occurred on the 23rd. With the warm temperatures during March 2024...most long term climate sites have reported below normal snowfall. Although El Nino has begun to weaken...we are still seeing its influence manifested in very intense southern stream storm systems that gather Gulf of Mexico moisture and then try to head up the east coast, as was the event unfolding at the time of this issuance. After that...it looks like early April 2024 will be characterized by a negative North Atlantic Oscillation (NAO) Index. This should promote a lot of upper level blocking downstream of New England in the North Atlantic which will likely deflect cold air from Canada southward into New England and New York State. At the same time...medium range climate indices call for the Pacific North America (PNA) Index to remain neutral to slightly positive. A positive PNA favors upper-level troughing across the southeastern United States. The combination of a negative NAO and somewhat positive PNA does increase the odds of east coast storminess. It remains to be seen where exactly the upper level blocking sets up and whether it will keep the coastal systems south and east of New England or allow them far enough north to impact the local area. Also...with near to below normal temperatures expected in early April...we may not be done with snow for this Winter...especially across the mountain regions. The official National Weather Service 6 to 10 day Outlook for 1-5 April 2024 seems to agree with this overall theme as it leans towards below normal temperatures and precipitation leaning above normal. Looking further out, the temperature outlooks favor warming towards mid April with near normal precipitation chances. ...IN CONCLUSION... In summary, the active weather pattern combined with residual snowpack and below normal storage supports an above normal risk of flooding through mid April. The potential for rapid runoff remains elevated until the seasonal green-up is underway. We do not anticipate large scale water supply issues heading into Spring. It is important to note that major flooding does not occur from snowmelt alone. Rainfall, how much and in how short a period of time, is the most important factor in determining the severity of flooding particularly before green-up has begun. These outlooks will be issued every two weeks until the end of the snow melt season, and will assess the potential for flooding based on a number of factors. The next Spring Flood Outlook will be issued on Thursday, April 11th. $$