NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260728_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 07/28 00Z 0.15 2204  75  78  15 0.00
Tue 07/28 01Z 0.16 2205  76  75  15 0.00
Tue 07/28 02Z 0.17 2106  77  70  15 0.00
Tue 07/28 03Z 0.13 1907  80  69  15 0.00
Tue 07/28 04Z 0.16 2009  82  72  15 0.00
Tue 07/28 05Z 0.20 2011  83  73  14 0.07
Tue 07/28 06Z 0.23 2112  85  75  14 0.03
Tue 07/28 07Z 0.18 2012  83  74  15 0.01
Tue 07/28 08Z 0.17 2013  80  75  15 0.00
Tue 07/28 09Z 0.09 1913  79  72  15 0.00
Tue 07/28 10Z 0.09 1914  78  71  15 0.00
Tue 07/28 11Z 0.05 1814  78  69  15 0.00
Tue 07/28 12Z 0.03 1814  80  70  15 0.00
Tue 07/28 13Z 0.02 1714  81  72  15 0.00
Tue 07/28 14Z 0.05 1714  82  72  15 0.00
Tue 07/28 15Z 0.08 1713  84  74  15 0.00
Tue 07/28 16Z 0.17 1615  88  74  15 0.00
Tue 07/28 17Z 0.33 1616  91  76  15 0.00
Tue 07/28 18Z 0.60 1617  92  77  15 0.06
Tue 07/28 19Z 0.75 1618  92  77  15 0.10
Tue 07/28 20Z 0.36 1620  92  73  15 0.03
Tue 07/28 21Z 0.16 1724  92  76  15 0.02
Tue 07/28 22Z 0.10 1722  94  79  15 0.01
Tue 07/28 23Z 0.09 1722  94  77  14 0.01
Wed 07/29 00Z 0.08 1822  96  79  14 0.01
Wed 07/29 01Z 0.08 1724  97  80  14 0.02
Wed 07/29 02Z 0.10 1722  96  74  14 0.04
Wed 07/29 03Z 0.10 1723  96  72  14 0.02
Wed 07/29 04Z 0.12 1723  94  70  14 0.02
Wed 07/29 05Z 0.17 1624  89  71  14 0.01
Wed 07/29 06Z 0.23 1625  85  70  14 0.01
Wed 07/29 07Z 0.31 1526  84  72  14 0.01
Wed 07/29 08Z 0.37 1527  82  72  14 0.01
Wed 07/29 09Z 0.42 1429  82  70  14 0.01
Wed 07/29 10Z 0.49 1430  78  73  14 0.01
Wed 07/29 11Z 0.56 1332  78  75  14 0.01
Wed 07/29 12Z 0.61 1333  79  74  13 0.01
Wed 07/29 13Z 0.68 1334  80  76  13 0.01
Wed 07/29 14Z 0.69 1333  77  80  13 0.00
Wed 07/29 15Z 0.72 1233  72  79  13 0.00
Wed 07/29 16Z 0.79 1232  71  79  13 0.00
Wed 07/29 17Z 0.99 1230  72  78  12 0.00
Wed 07/29 18Z 1.26 1129  72  78  12 0.00
Wed 07/29 19Z 1.01 1130  75  81  12 0.01
Wed 07/29 20Z 0.99 1031  77  81  12 0.01
Wed 07/29 21Z 1.00 1032  78  81  12 0.01
Wed 07/29 22Z 0.94 1032  81  86  12 0.02
Wed 07/29 23Z 0.90 1033  84  88  12 0.03
Thu 07/30 00Z 0.84 1033  88  89  12 0.03
Thu 07/30 01Z 0.82 1033  89  88  13 0.05
Thu 07/30 02Z 0.79 1033  91  92  13 0.05
Thu 07/30 03Z 0.74 1033  89  89  13 0.05
Thu 07/30 04Z 0.67 1031  91  86  13 0.04
Thu 07/30 05Z 0.62 1130  92  82  13 0.03
Thu 07/30 06Z 0.58 1129  93  81  13 0.03
Thu 07/30 07Z 0.54 1128  92  81  13 0.04
Thu 07/30 08Z 0.49 1125  92  77  13 0.03
Thu 07/30 09Z 0.47 1123  94  79  13 0.03
Thu 07/30 10Z 0.46 1122  95  84  13 0.03
Thu 07/30 11Z 0.41 1119  96  78  13 0.03

Run total areal avg QPF for the greens is: 1.06 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