Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260323_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)
=== ===== === ==== ==== === === === ====
Mon 03/23 00Z 0.11 3311  96  48  -2 0.00
Mon 03/23 01Z 0.05 3311  95  29  -2 0.00
Mon 03/23 02Z 0.06 3311  93  19  -2 0.00
Mon 03/23 03Z 0.03 3411  92  17  -3 0.00
Mon 03/23 04Z 0.06 0010  92  15  -3 0.00
Mon 03/23 05Z 0.12 0210  91  13  -3 0.00
Mon 03/23 06Z 0.14 0308  91  11  -4 0.00
Mon 03/23 07Z 0.18 0509  91  10  -4 0.00
Mon 03/23 08Z 0.23 0510  92  10  -4 0.00
Mon 03/23 09Z 0.21 0608  93  12  -5 0.00
Mon 03/23 10Z 0.25 0709  94  13  -6 0.00
Mon 03/23 11Z 0.30 0710  96  15  -7 0.00
Mon 03/23 12Z 0.34 0810  97  17  -7 0.01
Mon 03/23 13Z 0.33 0809  98  17  -8 0.01
Mon 03/23 14Z 0.35 0609  97  20  -8 0.00
Mon 03/23 15Z 0.39 0608  97  21  -8 0.00
Mon 03/23 16Z 0.35 0605  97  34  -8 0.00
Mon 03/23 17Z 0.15 0502  97  41  -8 0.00
Mon 03/23 18Z 0.09 0201  97  45  -8 0.00
Mon 03/23 19Z 0.07 3203  97  39  -8 0.01
Mon 03/23 20Z 0.12 3207  97  37  -8 0.01
Mon 03/23 21Z 0.15 3210  95  40  -8 0.01
Mon 03/23 22Z 0.15 3312  95  42  -8 0.01
Mon 03/23 23Z 0.12 3316  95  40  -8 0.01
Tue 03/24 00Z 0.09 3420  96  51  -9 0.01
Tue 03/24 01Z 0.08 3422  96  64  -9 0.01
Tue 03/24 02Z 0.10 3425  94  72  -9 0.01
Tue 03/24 03Z 0.11 3425  89  72 -10 0.01
Tue 03/24 04Z 0.09 3425  84  71 -10 0.00
Tue 03/24 05Z 0.07 3425  84  57 -11 0.00
Tue 03/24 06Z 0.08 3423  86  44 -11 0.00
Tue 03/24 07Z 0.13 3421  87  35 -11 0.00
Tue 03/24 08Z 0.17 3320  88  22 -11 0.00
Tue 03/24 09Z 0.13 3418  87   5 -11 0.00
Tue 03/24 10Z 0.19 3318  87   3 -12 0.00
Tue 03/24 11Z 0.19 3318  85   7 -12 0.00
Tue 03/24 12Z 0.18 3318  82   9 -12 0.00
Tue 03/24 13Z 0.19 3315  80  10 -12 0.00
Tue 03/24 14Z 0.18 3312  73   9 -12 0.00
Tue 03/24 15Z 0.87 3111  76   7 -12 0.00
Tue 03/24 16Z 0.82 2908  69   5 -11 0.00
Tue 03/24 17Z 0.93 2708  60   7 -10 0.00
Tue 03/24 18Z 0.81 2508  50   7  -9 0.00
Tue 03/24 19Z 0.51 2310  44   6  -8 0.00
Tue 03/24 20Z 0.89 2314  44   5  -8 0.00
Tue 03/24 21Z 1.01 2417  46   8  -8 0.00
Tue 03/24 22Z 0.97 2421  49  10  -7 0.00
Tue 03/24 23Z 1.08 2426  45  25  -7 0.00
Wed 03/25 00Z 1.54 2531  39  47  -7 0.00
Wed 03/25 01Z 2.45 2632  44  82  -8 0.00
Wed 03/25 02Z 5.54 2730  61  85  -9 0.00
Wed 03/25 03Z 1.77 2729  79  36 -10 0.00
Wed 03/25 04Z 1.13 2828  84   8  -9 0.00
Wed 03/25 05Z 0.95 2827  80   7  -9 0.00
Wed 03/25 06Z 0.73 2826  72   6  -8 0.00
Wed 03/25 07Z 0.54 2824  62   7  -7 0.00
Wed 03/25 08Z 0.51 2923  60   6  -7 0.00
Wed 03/25 09Z 0.46 2922  55   7  -6 0.00
Wed 03/25 10Z 0.42 2921  53  10  -6 0.00
Wed 03/25 11Z 0.35 2919  44   9  -5 0.00

Run total areal avg QPF for the Central_Greens is: 0.11 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