NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260219_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 02/19 00Z 0.11 0110  44  41  -5 0.00
Thu 02/19 01Z 0.20 0213  48  61  -5 0.00
Thu 02/19 02Z 0.25 0314  53  71  -6 0.00
Thu 02/19 03Z 0.24 0314  53  72  -6 0.00
Thu 02/19 04Z 0.21 0313  50  65  -6 0.00
Thu 02/19 05Z 0.14 0210  44  58  -6 0.00
Thu 02/19 06Z 0.15 0310  39  54  -5 0.00
Thu 02/19 07Z 0.14 0309  34  48  -5 0.00
Thu 02/19 08Z 0.12 0307  30  48  -5 0.00
Thu 02/19 09Z 0.09 0305  28  37  -5 0.00
Thu 02/19 10Z 0.07 0304  25  24  -5 0.00
Thu 02/19 11Z 0.06 0304  23  15  -5 0.00
Thu 02/19 12Z 0.08 0404  23  15  -4 0.00
Thu 02/19 13Z 0.06 0403  24  17  -4 0.00
Thu 02/19 14Z 0.06 0602  25  18  -4 0.00
Thu 02/19 15Z 0.05 0802  26  17  -4 0.00
Thu 02/19 16Z 0.03 1101  29  32  -4 0.00
Thu 02/19 17Z 0.01 1701  33  42  -4 0.00
Thu 02/19 18Z 0.03 1803  36  48  -4 0.00
Thu 02/19 19Z 0.04 1903  39  59  -4 0.00
Thu 02/19 20Z 0.07 2003  45  53  -4 0.00
Thu 02/19 21Z 0.09 2104  49  50  -4 0.00
Thu 02/19 22Z 0.15 2306  54  48  -4 0.00
Thu 02/19 23Z 0.13 2305  60  47  -4 0.00
Fri 02/20 00Z 0.07 2203  70  40  -3 0.00
Fri 02/20 01Z 0.03 1803  76  28  -3 0.00
Fri 02/20 02Z 0.07 1905  79  10  -4 0.00
Fri 02/20 03Z 0.11 2006  84  12  -4 0.00
Fri 02/20 04Z 0.11 2007  88  13  -5 0.00
Fri 02/20 05Z 0.13 2007  92  10  -5 0.00
Fri 02/20 06Z 0.14 2107  92  10  -5 0.00
Fri 02/20 07Z 0.13 2007  89   8  -4 0.00
Fri 02/20 08Z 0.11 2007  86  10  -4 0.00
Fri 02/20 09Z 0.08 2006  82  16  -3 0.00
Fri 02/20 10Z 0.08 1906  79  30  -3 0.00
Fri 02/20 11Z 0.05 1806  77  33  -2 0.00
Fri 02/20 12Z 0.02 1707  78  35  -2 0.00
Fri 02/20 13Z 0.03 1609  79  35  -2 0.00
Fri 02/20 14Z 0.02 1612  82  31  -2 0.00
Fri 02/20 15Z 0.03 1613  81  31  -2 0.00
Fri 02/20 16Z 0.02 1615  81  36  -3 0.00
Fri 02/20 17Z 0.05 1615  75  40  -2 0.00
Fri 02/20 18Z 0.05 1616  71  65  -1 0.00
Fri 02/20 19Z 0.11 1516  77  91   0 0.00
Fri 02/20 20Z 0.14 1417  90  97  -1 0.02
Fri 02/20 21Z 0.19 1421  96  98   0 0.08
Fri 02/20 22Z 0.25 1323  95  99  -1 0.14
Fri 02/20 23Z 0.31 1327  95  99  -1 0.14
Sat 02/21 00Z 0.32 1329  95  99  -1 0.10
Sat 02/21 01Z 0.32 1329  95  97  -2 0.06
Sat 02/21 02Z 0.30 1328  96  78  -2 0.03
Sat 02/21 03Z 0.27 1425  96  95  -3 0.04
Sat 02/21 04Z 0.24 1422  95  93  -4 0.06
Sat 02/21 05Z 0.17 1519  95  94  -6 0.05
Sat 02/21 06Z 0.10 1517  95  93  -6 0.02
Sat 02/21 07Z 0.04 1715  96  93  -6 0.02
Sat 02/21 08Z 0.09 1812  96  93  -6 0.02
Sat 02/21 09Z 0.15 1911  96  94  -6 0.02
Sat 02/21 10Z 0.20 2010  97  96  -7 0.02
Sat 02/21 11Z 0.25 2111  98  98  -7 0.02

Run total areal avg QPF for the Central_Greens is: 0.84 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1