Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20251110_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)
=== ===== === ==== ==== === === === ====
Mon 11/10 18Z 0.10 0903 100  85   2 0.00
Mon 11/10 19Z 0.09 0504  99  91   2 0.04
Mon 11/10 20Z 0.07 0206  99  98   2 0.07
Mon 11/10 21Z 0.04 3508  98  96   1 0.07
Mon 11/10 22Z 0.09 3209  98  96   0 0.09
Mon 11/10 23Z 0.19 3013  97  97   0 0.12
Tue 11/11 00Z 0.24 3118  94  91  -1 0.06
Tue 11/11 01Z 0.23 3118  91  73  -1 0.01
Tue 11/11 02Z 0.28 3018  94  54  -3 0.01
Tue 11/11 03Z 0.40 2921  95  32  -4 0.01
Tue 11/11 04Z 0.42 2920  96  19  -5 0.01
Tue 11/11 05Z 0.38 2916  97  10  -5 0.01
Tue 11/11 06Z 0.39 2815  96   7  -6 0.01
Tue 11/11 07Z 0.42 2816  95   5  -6 0.01
Tue 11/11 08Z 0.46 2716  94   6  -7 0.01
Tue 11/11 09Z 0.55 2717  95   9  -9 0.01
Tue 11/11 10Z 0.58 2717  95  14  -9 0.01
Tue 11/11 11Z 0.69 2617  96  20 -10 0.01
Tue 11/11 12Z 0.85 2618  96  26 -11 0.01
Tue 11/11 13Z 1.04 2717  96  38 -11 0.01
Tue 11/11 14Z 1.64 2818  96  50 -11 0.01
Tue 11/11 15Z 2.50 2717  95  70 -11 0.01
Tue 11/11 16Z 3.52 2716  95  88 -11 0.01
Tue 11/11 17Z 3.17 2616  94  91 -10 0.02
Tue 11/11 18Z 4.18 2618  94  87 -10 0.02
Tue 11/11 19Z 3.72 2621  95  81 -10 0.02
Tue 11/11 20Z 2.51 2723  94  75 -10 0.02
Tue 11/11 21Z 1.43 2725  92  76 -10 0.02
Tue 11/11 22Z 1.63 2728  91  75 -10 0.01
Tue 11/11 23Z 1.53 2831  91  71 -10 0.01
Wed 11/12 00Z 1.47 2831  91  61 -10 0.00
Wed 11/12 01Z 1.19 2831  84  66 -10 0.00
Wed 11/12 02Z 1.29 2830  86  70 -10 0.00
Wed 11/12 03Z 1.32 2830  89  36 -10 0.00
Wed 11/12 04Z 1.10 2828  90  20  -9 0.00
Wed 11/12 05Z 0.95 2828  89  20  -9 0.00
Wed 11/12 06Z 0.82 2828  86  25  -8 0.00
Wed 11/12 07Z 0.68 2725  80  26  -7 0.00
Wed 11/12 08Z 0.68 2724  80  26  -6 0.00
Wed 11/12 09Z 0.63 2622  84  28  -6 0.00
Wed 11/12 10Z 0.55 2619  88  64  -6 0.00
Wed 11/12 11Z 0.49 2518  87  85  -5 0.00
Wed 11/12 12Z 0.48 2417  82  88  -6 0.00
Wed 11/12 13Z 0.45 2315  91  90  -6 0.01
Wed 11/12 14Z 0.41 2215  94  91  -6 0.01
Wed 11/12 15Z 0.49 2214  94  91  -7 0.01
Wed 11/12 16Z 0.58 2312  94  89  -7 0.01
Wed 11/12 17Z 0.68 2311  93  86  -7 0.00
Wed 11/12 18Z 0.57 2311  91  89  -6 0.00
Wed 11/12 19Z 0.45 2311  89  93  -6 0.00
Wed 11/12 20Z 0.51 2413  93  92  -6 0.00
Wed 11/12 21Z 0.59 2415  95  91  -6 0.00
Wed 11/12 22Z 0.58 2516  95  90  -5 0.00
Wed 11/12 23Z 0.57 2617  94  88  -5 0.01
Thu 11/13 00Z 0.56 2517  95  86  -5 0.01
Thu 11/13 01Z 0.61 2618  96  84  -5 0.02
Thu 11/13 02Z 0.61 2718  96  82  -4 0.01
Thu 11/13 03Z 0.54 2717  96  82  -4 0.01
Thu 11/13 04Z 0.45 2714  96  86  -4 0.01
Thu 11/13 05Z 0.43 2613  97  91  -4 0.02

Run total areal avg QPF for the Central_Greens is: 0.86 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