NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260323_1800
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)
=== ===== === ==== ==== === === === ====
Mon 03/23 18Z 0.10 3205  97  22  -8 0.00
Mon 03/23 19Z 0.25 3208  96  22  -8 0.00
Mon 03/23 20Z 0.27 3211  95  24  -8 0.00
Mon 03/23 21Z 0.30 3315  93  26  -9 0.00
Mon 03/23 22Z 0.30 3318  92  23  -9 0.00
Mon 03/23 23Z 0.28 3420  91  21  -9 0.00
Tue 03/24 00Z 0.23 3421  92  20 -10 0.00
Tue 03/24 01Z 0.22 3422  90  19 -10 0.00
Tue 03/24 02Z 0.25 3423  88  19 -10 0.00
Tue 03/24 03Z 0.29 3424  89  20 -10 0.00
Tue 03/24 04Z 0.29 3424  90  16 -10 0.00
Tue 03/24 05Z 0.26 3422  90  13 -11 0.00
Tue 03/24 06Z 0.25 3421  91  12 -11 0.00
Tue 03/24 07Z 0.29 3420  91   8 -11 0.00
Tue 03/24 08Z 0.30 3419  90   4 -11 0.01
Tue 03/24 09Z 0.27 3419  89   4 -11 0.00
Tue 03/24 10Z 0.23 3418  86   5 -12 0.00
Tue 03/24 11Z 0.20 3417  84   8 -12 0.00
Tue 03/24 12Z 0.19 3416  83  10 -12 0.00
Tue 03/24 13Z 0.23 3314  84  11 -13 0.00
Tue 03/24 14Z 0.48 3211  83  13 -13 0.00
Tue 03/24 15Z 0.75 3010  78  12 -12 0.00
Tue 03/24 16Z 0.51 2808  69   9 -11 0.00
Tue 03/24 17Z 0.95 2708  64   7 -11 0.00
Tue 03/24 18Z 0.88 2507  56   5 -10 0.00
Tue 03/24 19Z 0.75 2408  48   5  -9 0.00
Tue 03/24 20Z 0.66 2310  46   6  -8 0.00
Tue 03/24 21Z 0.65 2413  47   8  -8 0.00
Tue 03/24 22Z 0.79 2417  50  16  -8 0.00
Tue 03/24 23Z 0.86 2420  49  32  -7 0.00
Wed 03/25 00Z 1.13 2425  47  35  -7 0.00
Wed 03/25 01Z 2.11 2529  47  66  -8 0.00
Wed 03/25 02Z 5.62 2629  61  80  -9 0.00
Wed 03/25 03Z 2.01 2731  82  90 -10 0.01
Wed 03/25 04Z 1.33 2828  90  65 -10 0.01
Wed 03/25 05Z 1.10 2926  91  11 -10 0.00
Wed 03/25 06Z 1.03 2925  90  14 -10 0.01
Wed 03/25 07Z 0.89 2924  85   7 -10 0.00
Wed 03/25 08Z 0.84 2924  82   6  -9 0.00
Wed 03/25 09Z 0.76 2922  81  10  -9 0.00
Wed 03/25 10Z 0.64 2921  78  23  -9 0.00
Wed 03/25 11Z 0.51 2819  68  40  -8 0.00
Wed 03/25 12Z 0.48 2818  58  31  -7 0.00
Wed 03/25 13Z 0.39 2815  50  21  -6 0.00
Wed 03/25 14Z 0.35 2714  46  12  -5 0.00
Wed 03/25 15Z 0.34 2513  42  12  -5 0.00
Wed 03/25 16Z 0.36 2413  38  14  -5 0.00
Wed 03/25 17Z 0.40 2314  33   9  -5 0.00
Wed 03/25 18Z 0.46 2216  29  21  -4 0.00
Wed 03/25 19Z 0.51 2216  31  47  -4 0.00
Wed 03/25 20Z 0.76 2218  43  76  -4 0.00
Wed 03/25 21Z 0.85 2221  54  93  -4 0.00
Wed 03/25 22Z 1.37 2224  63  92  -4 0.00
Wed 03/25 23Z 5.15 2227  68  89  -5 0.00
Thu 03/26 00Z 1.86 2229  82  89  -5 0.00
Thu 03/26 01Z 0.77 2228  92  84  -4 0.01
Thu 03/26 02Z 0.68 2229  88  86  -3 0.01
Thu 03/26 03Z 0.77 2235  93  74  -3 0.01
Thu 03/26 04Z 0.70 2234  90  93  -2 0.01
Thu 03/26 05Z 0.75 2334  89  92  -1 0.00

Run total areal avg QPF for the greens is: 0.08 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