NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260422_1800
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)
=== ===== === ==== ==== === === === ====
Wed 04/22 18Z 0.25 1906  92  73   0 0.00
Wed 04/22 19Z 0.14 1808  94  70   0 0.00
Wed 04/22 20Z 0.22 1911  96  52   0 0.00
Wed 04/22 21Z 0.23 2011  96  42   0 0.00
Wed 04/22 22Z 0.29 2112  98  80   0 0.00
Wed 04/22 23Z 0.25 2210  97  50   1 0.01
Thu 04/23 00Z 0.27 2410  97  51   1 0.00
Thu 04/23 01Z 0.26 2610  97  27   2 0.00
Thu 04/23 02Z 0.27 2711  96  24   2 0.00
Thu 04/23 03Z 0.27 2811  94  17   2 0.00
Thu 04/23 04Z 0.25 2911  92  38   2 0.00
Thu 04/23 05Z 0.27 2913  90  59   1 0.00
Thu 04/23 06Z 0.32 2914  89  71   1 0.00
Thu 04/23 07Z 0.35 3016  88  78   1 0.00
Thu 04/23 08Z 0.42 3018  87  80   1 0.00
Thu 04/23 09Z 0.42 3020  87  79   1 0.00
Thu 04/23 10Z 0.40 3122  88  74   0 0.00
Thu 04/23 11Z 0.34 3223  89  64   0 0.00
Thu 04/23 12Z 0.28 3223  88  28  -1 0.00
Thu 04/23 13Z 0.27 3323  89   8  -2 0.00
Thu 04/23 14Z 0.72 3323  90   8  -3 0.00
Thu 04/23 15Z 3.36 3223  85  10  -3 0.00
Thu 04/23 16Z 4.96 3223  86   9  -3 0.00
Thu 04/23 17Z 5.59 3223  81  10  -2 0.00
Thu 04/23 18Z 5.43 3222  72   8  -1 0.00
Thu 04/23 19Z 5.43 3221  67   8  -1 0.00
Thu 04/23 20Z 4.86 3220  63   7  -1 0.00
Thu 04/23 21Z 4.13 3220  57   6  -1 0.00
Thu 04/23 22Z 2.65 3321  54   5  -1 0.00
Thu 04/23 23Z 0.70 3322  53   3  -1 0.00
Fri 04/24 00Z 0.34 3423  54   2  -2 0.00
Fri 04/24 01Z 0.28 3423  54   1  -2 0.00
Fri 04/24 02Z 0.18 3421  54   2  -3 0.00
Fri 04/24 03Z 0.19 3418  58   3  -3 0.00
Fri 04/24 04Z 0.17 3514  62   4  -4 0.00
Fri 04/24 05Z 0.10 3511  69   6  -4 0.00
Fri 04/24 06Z 0.05 3410  74   8  -4 0.00
Fri 04/24 07Z 0.11 3311  76   9  -5 0.00
Fri 04/24 08Z 0.10 3412  76  10  -5 0.00
Fri 04/24 09Z 0.07 3414  76  11  -5 0.00
Fri 04/24 10Z 0.08 3416  73  12  -5 0.00
Fri 04/24 11Z 0.07 3417  70  10  -5 0.00
Fri 04/24 12Z 0.06 3416  73   9  -5 0.00
Fri 04/24 13Z 0.04 3413  76  18  -5 0.00
Fri 04/24 14Z 0.08 3511  74  33  -5 0.00
Fri 04/24 15Z 0.44 3309  73  45  -5 0.00
Fri 04/24 16Z 0.41 3409  70  45  -4 0.00
Fri 04/24 17Z 0.80 3308  66  43  -3 0.00
Fri 04/24 18Z 1.11 3309  61  38  -3 0.00
Fri 04/24 19Z 1.27 3310  56  29  -2 0.00
Fri 04/24 20Z 1.20 3311  47  27  -2 0.00
Fri 04/24 21Z 0.59 3413  39  28  -2 0.00
Fri 04/24 22Z 0.22 3413  39  27  -1 0.00
Fri 04/24 23Z 0.10 3512  46  16  -2 0.00
Sat 04/25 00Z 0.21 0012  55   9  -2 0.00
Sat 04/25 01Z 0.35 0213  63   6  -2 0.00
Sat 04/25 02Z 0.46 0312  65   4  -3 0.00
Sat 04/25 03Z 0.46 0411  69   7  -3 0.00
Sat 04/25 04Z 0.35 0509  71  20  -3 0.00
Sat 04/25 05Z 0.33 0610  70  30  -3 0.00

Run total areal avg QPF for the Central_Greens is: 0.01 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