NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260817_1200
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 12Z 0.31 2313  99  94  14 0.00
Mon 08/17 13Z 0.33 2413  99  90  14 0.06
Mon 08/17 14Z 0.32 2412  99  88  14 0.04
Mon 08/17 15Z 0.29 2411  98  86  14 0.03
Mon 08/17 16Z 0.32 2512  98  88  14 0.06
Mon 08/17 17Z 0.32 2711  98  87  14 0.03
Mon 08/17 18Z 0.29 2809  98  89  14 0.03
Mon 08/17 19Z 0.25 2908  97  84  14 0.02
Mon 08/17 20Z 0.20 3006  95  80  14 0.00
Mon 08/17 21Z 0.15 3005  94  71  14 0.01
Mon 08/17 22Z 0.12 3003  93  64  14 0.03
Mon 08/17 23Z 0.12 3103  93  56  14 0.03
Tue 08/18 00Z 0.12 3104  93  57  14 0.05
Tue 08/18 01Z 0.12 3203  93  63  14 0.05
Tue 08/18 02Z 0.09 3303  92  80  14 0.03
Tue 08/18 03Z 0.08 3302  91  80  14 0.02
Tue 08/18 04Z 0.06 3101  92  71  14 0.01
Tue 08/18 05Z 0.06 3101  93  65  13 0.00
Tue 08/18 06Z 0.05 3201  93  47  13 0.01
Tue 08/18 07Z 0.03 3301  93  44  13 0.00
Tue 08/18 08Z 0.04 3202  93  37  13 0.00
Tue 08/18 09Z 0.06 3102  93  28  13 0.00
Tue 08/18 10Z 0.08 3103  93  15  13 0.00
Tue 08/18 11Z 0.08 3104  92   8  12 0.00
Tue 08/18 12Z 0.08 3204  92   5  12 0.00
Tue 08/18 13Z 0.08 3204  92   4  12 0.00
Tue 08/18 14Z 0.06 3303  92   4  12 0.00
Tue 08/18 15Z 0.04 3201  92   4  12 0.00
Tue 08/18 16Z 0.09 2702  94   4  12 0.00
Tue 08/18 17Z 0.12 2903  93   4  12 0.01
Tue 08/18 18Z 0.19 3006  93   4  12 0.01
Tue 08/18 19Z 0.18 2905  89   4  12 0.00
Tue 08/18 20Z 0.16 2704  82   4  13 0.00
Tue 08/18 21Z 0.15 2604  79   4  13 0.00
Tue 08/18 22Z 0.24 2806  81   5  12 0.00
Tue 08/18 23Z 0.22 2907  83   5  12 0.00
Wed 08/19 00Z 0.16 3006  82   5  12 0.00
Wed 08/19 01Z 0.14 3005  81   7  12 0.00
Wed 08/19 02Z 0.12 3004  80   8  12 0.00
Wed 08/19 03Z 0.13 2904  80   7  12 0.00
Wed 08/19 04Z 0.16 2805  81   6  11 0.00
Wed 08/19 05Z 0.17 2705  77   7  12 0.00
Wed 08/19 06Z 0.19 2806  75   7  12 0.00
Wed 08/19 07Z 0.18 2806  73   8  12 0.00
Wed 08/19 08Z 0.16 2806  71  10  11 0.00
Wed 08/19 09Z 0.14 2705  67  13  12 0.00
Wed 08/19 10Z 0.13 2705  65  17  11 0.00
Wed 08/19 11Z 0.15 2705  64  20  11 0.00
Wed 08/19 12Z 0.15 2605  61  25  12 0.00
Wed 08/19 13Z 0.11 2504  57  34  12 0.00
Wed 08/19 14Z 0.15 2406  58  42  12 0.00
Wed 08/19 15Z 0.20 2407  59  40  12 0.00
Wed 08/19 16Z 0.25 2408  58  51  12 0.00
Wed 08/19 17Z 0.32 2509  58  59  12 0.00
Wed 08/19 18Z 0.37 2509  58  64  12 0.00
Wed 08/19 19Z 0.40 2608  61  71  13 0.00
Wed 08/19 20Z 0.53 2509  68  78  13 0.00
Wed 08/19 21Z 0.48 2509  74  79  13 0.00
Wed 08/19 22Z 0.53 2410  82  79  13 0.00
Wed 08/19 23Z 0.54 2513  89  78  12 0.02

Run total areal avg QPF for the greens is: 0.55 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