NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260419_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)
=== ===== === ==== ==== === === === ====
Sun 04/19 00Z 0.03 1623  80   7   8 0.00
Sun 04/19 01Z 0.06 1725  81  11   9 0.00
Sun 04/19 02Z 0.11 1827  78  11  10 0.00
Sun 04/19 03Z 0.20 1929  78  16  10 0.00
Sun 04/19 04Z 0.30 1931  77  44  10 0.00
Sun 04/19 05Z 0.42 2134  84  69  10 0.01
Sun 04/19 06Z 0.49 2134  94  88   9 0.05
Sun 04/19 07Z 0.52 2229  98  97   8 0.10
Sun 04/19 08Z 0.52 2325  98  95   7 0.05
Sun 04/19 09Z 0.45 2419  98  93   6 0.03
Sun 04/19 10Z 0.42 2416  98  91   6 0.03
Sun 04/19 11Z 0.50 2617  98  92   4 0.02
Sun 04/19 12Z 0.40 2813  98  89   3 0.03
Sun 04/19 13Z 0.32 3114  97  96   1 0.02
Sun 04/19 14Z 0.50 3120  98  99   0 0.05
Sun 04/19 15Z 0.30 3224  97 100  -1 0.11
Sun 04/19 16Z 0.34 3123  95  99  -2 0.13
Sun 04/19 17Z 0.35 3224  97  99  -4 0.07
Sun 04/19 18Z 0.41 3123  95  98  -5 0.07
Sun 04/19 19Z 0.51 3124  95  97  -6 0.04
Sun 04/19 20Z 0.56 3124  95  94  -6 0.03
Sun 04/19 21Z 0.47 3122  94  90  -6 0.03
Sun 04/19 22Z 0.34 3220  81  40  -6 0.02
Sun 04/19 23Z 0.43 3120  79  18  -5 0.00
Mon 04/20 00Z 0.54 3021  90  32  -5 0.00
Mon 04/20 01Z 0.69 2921  95  52  -5 0.02
Mon 04/20 02Z 0.91 2923  95  65  -6 0.02
Mon 04/20 03Z 0.87 3024  86  50  -6 0.01
Mon 04/20 04Z 0.80 3022  79  24  -6 0.00
Mon 04/20 05Z 0.73 2920  70  33  -6 0.00
Mon 04/20 06Z 0.84 2919  67  48  -7 0.00
Mon 04/20 07Z 0.82 2818  68  54  -7 0.00
Mon 04/20 08Z 0.85 2718  71  67  -7 0.00
Mon 04/20 09Z 0.76 2817  77  81  -7 0.00
Mon 04/20 10Z 0.63 2916  88  87  -8 0.00
Mon 04/20 11Z 0.47 3014  94  78  -8 0.02
Mon 04/20 12Z 0.36 3012  93  61  -9 0.01
Mon 04/20 13Z 0.38 3110  92  47  -9 0.00
Mon 04/20 14Z 0.89 3209  90  58  -9 0.00
Mon 04/20 15Z 0.86 3209  86  34  -9 0.00
Mon 04/20 16Z 1.38 3209  81  41  -9 0.00
Mon 04/20 17Z 2.22 3209  76  41  -9 0.00
Mon 04/20 18Z 2.93 3110  71  41  -9 0.00
Mon 04/20 19Z 3.90 3111  66  36  -9 0.00
Mon 04/20 20Z 4.24 3112  66  36  -9 0.00
Mon 04/20 21Z 3.51 3112  68  39  -9 0.00
Mon 04/20 22Z 2.35 3213  69  43  -9 0.00
Mon 04/20 23Z 1.06 3314  69  42 -10 0.00
Tue 04/21 00Z 0.57 3315  67  36 -10 0.00
Tue 04/21 01Z 0.70 3316  64  31 -11 0.00
Tue 04/21 02Z 0.93 3217  62  27 -11 0.00
Tue 04/21 03Z 0.92 3218  61  20 -12 0.00
Tue 04/21 04Z 0.72 3217  60  12 -12 0.00
Tue 04/21 05Z 0.62 3316  60   9 -12 0.00
Tue 04/21 06Z 0.46 3315  60  10 -12 0.00
Tue 04/21 07Z 0.30 3314  57  12 -12 0.00
Tue 04/21 08Z 0.19 3313  53  10 -12 0.00
Tue 04/21 09Z 0.10 3411  49  11 -12 0.00
Tue 04/21 10Z 0.12 3310  48  10 -12 0.00
Tue 04/21 11Z 0.14 3308  48   7 -11 0.00

Run total areal avg QPF for the Central_Greens is: 0.97 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