NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260817_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 08/17 18Z 0.27 2706  97  80  14 0.00
Mon 08/17 19Z 0.16 2804  95  71  15 0.00
Mon 08/17 20Z 0.13 2903  93  76  15 0.01
Mon 08/17 21Z 0.14 3004  93  72  15 0.02
Mon 08/17 22Z 0.15 3105  93  68  15 0.03
Mon 08/17 23Z 0.11 3305  93  65  14 0.06
Tue 08/18 00Z 0.09 0004  93  72  14 0.01
Tue 08/18 01Z 0.07 0003  91  74  14 0.03
Tue 08/18 02Z 0.09 0103  89  84  14 0.13
Tue 08/18 03Z 0.09 0303  91  86  14 0.07
Tue 08/18 04Z 0.09 0502  92  81  14 0.01
Tue 08/18 05Z 0.06 0101  94  73  14 0.01
Tue 08/18 06Z 0.05 0002  94  58  14 0.01
Tue 08/18 07Z 0.05 0004  95  49  14 0.01
Tue 08/18 08Z 0.04 0005  93  47  13 0.01
Tue 08/18 09Z 0.03 0005  92  35  13 0.01
Tue 08/18 10Z 0.03 3506  90  32  13 0.00
Tue 08/18 11Z 0.03 3505  88  27  13 0.00
Tue 08/18 12Z 0.03 3505  88  23  13 0.00
Tue 08/18 13Z 0.02 3505  89  15  13 0.00
Tue 08/18 14Z 0.02 0004  89   8  13 0.00
Tue 08/18 15Z 0.02 3503  90   4  12 0.00
Tue 08/18 16Z 0.04 3402  91   4  12 0.01
Tue 08/18 17Z 0.05 3101  91   3  13 0.01
Tue 08/18 18Z 0.12 2903  91   3  13 0.01
Tue 08/18 19Z 0.13 2904  87   3  13 0.00
Tue 08/18 20Z 0.16 2905  86   3  13 0.00
Tue 08/18 21Z 0.23 2907  83   3  13 0.00
Tue 08/18 22Z 0.11 2903  78   3  13 0.00
Tue 08/18 23Z 0.11 2803  78   3  13 0.00
Wed 08/19 00Z 0.16 2704  79   7  12 0.00
Wed 08/19 01Z 0.13 2804  79   6  12 0.00
Wed 08/19 02Z 0.17 2705  81  11  12 0.00
Wed 08/19 03Z 0.15 2804  83   8  12 0.00
Wed 08/19 04Z 0.16 2704  87   6  11 0.00
Wed 08/19 05Z 0.21 2806  90   7  11 0.00
Wed 08/19 06Z 0.17 2805  91  12  11 0.00
Wed 08/19 07Z 0.18 2805  91  16  11 0.00
Wed 08/19 08Z 0.20 2806  91  14  11 0.00
Wed 08/19 09Z 0.18 2705  89  13  11 0.00
Wed 08/19 10Z 0.20 2707  87  11  11 0.00
Wed 08/19 11Z 0.20 2607  83  10  11 0.01
Wed 08/19 12Z 0.19 2507  75  23  12 0.00
Wed 08/19 13Z 0.22 2509  72  42  12 0.00
Wed 08/19 14Z 0.22 2509  70  58  12 0.00
Wed 08/19 15Z 0.23 2409  69  69  12 0.00
Wed 08/19 16Z 0.23 2409  66  64  13 0.00
Wed 08/19 17Z 0.31 2311  62  66  13 0.00
Wed 08/19 18Z 0.40 2314  57  55  14 0.00
Wed 08/19 19Z 0.49 2315  57  51  14 0.00
Wed 08/19 20Z 0.61 2415  70  50  14 0.00
Wed 08/19 21Z 1.85 2418  84  45  13 0.00
Wed 08/19 22Z 0.79 2519  92  34  13 0.01
Wed 08/19 23Z 0.68 2517  93  34  13 0.01
Thu 08/20 00Z 0.68 2518  93  50  13 0.01
Thu 08/20 01Z 0.63 2617  91  39  13 0.03
Thu 08/20 02Z 0.54 2616  87  33  13 0.01
Thu 08/20 03Z 0.48 2615  84  40  13 0.01
Thu 08/20 04Z 0.44 2715  80  32  13 0.01
Thu 08/20 05Z 0.39 2714  78  32  13 0.01

Run total areal avg QPF for the greens is: 0.56 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