NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260817_1200
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 08/17 12Z 0.33 2312  99  93  13 0.00
Mon 08/17 13Z 0.33 2313  98  90  14 0.02
Mon 08/17 14Z 0.34 2313  98  90  14 0.04
Mon 08/17 15Z 0.32 2312  98  81  14 0.03
Mon 08/17 16Z 0.34 2512  98  82  15 0.03
Mon 08/17 17Z 0.32 2711  98  81  15 0.02
Mon 08/17 18Z 0.26 2708  98  88  15 0.02
Mon 08/17 19Z 0.21 2906  97  86  15 0.02
Mon 08/17 20Z 0.14 2904  97  82  15 0.00
Mon 08/17 21Z 0.09 3102  96  84  14 0.02
Mon 08/17 22Z 0.07 3102  95  84  14 0.04
Mon 08/17 23Z 0.07 3201  95  75  15 0.04
Tue 08/18 00Z 0.08 3202  96  77  14 0.07
Tue 08/18 01Z 0.09 3502  95  81  14 0.07
Tue 08/18 02Z 0.10 3502  95  87  14 0.04
Tue 08/18 03Z 0.09 0001  95  85  14 0.03
Tue 08/18 04Z 0.07 3200  95  76  14 0.01
Tue 08/18 05Z 0.06 3200  96  72  14 0.01
Tue 08/18 06Z 0.05 3201  97  50  14 0.01
Tue 08/18 07Z 0.03 3501  97  41  14 0.00
Tue 08/18 08Z 0.02 3202  97  27  13 0.00
Tue 08/18 09Z 0.05 3102  97  14  13 0.00
Tue 08/18 10Z 0.07 3104  97  10  13 0.00
Tue 08/18 11Z 0.07 3104  96   7  13 0.00
Tue 08/18 12Z 0.06 3205  95   6  12 0.00
Tue 08/18 13Z 0.07 3204  94   5  12 0.00
Tue 08/18 14Z 0.06 3204  94   5  12 0.00
Tue 08/18 15Z 0.05 3001  95   4  12 0.00
Tue 08/18 16Z 0.09 2802  95   4  12 0.00
Tue 08/18 17Z 0.11 2903  94   4  12 0.01
Tue 08/18 18Z 0.17 3006  93   4  12 0.01
Tue 08/18 19Z 0.18 2906  89   5  13 0.00
Tue 08/18 20Z 0.17 2804  80   4  13 0.00
Tue 08/18 21Z 0.15 2603  76   5  13 0.00
Tue 08/18 22Z 0.23 2806  78   5  13 0.00
Tue 08/18 23Z 0.20 2907  81   5  12 0.00
Wed 08/19 00Z 0.14 3106  82   5  12 0.00
Wed 08/19 01Z 0.12 3005  81   6  12 0.00
Wed 08/19 02Z 0.10 3004  81   8  12 0.00
Wed 08/19 03Z 0.11 2904  80   7  12 0.00
Wed 08/19 04Z 0.16 2805  80   6  12 0.00
Wed 08/19 05Z 0.16 2805  77   7  12 0.00
Wed 08/19 06Z 0.19 2806  76   7  12 0.00
Wed 08/19 07Z 0.17 2806  72   8  12 0.00
Wed 08/19 08Z 0.16 2806  70  10  12 0.00
Wed 08/19 09Z 0.15 2705  67  11  12 0.00
Wed 08/19 10Z 0.14 2705  66  12  12 0.00
Wed 08/19 11Z 0.15 2705  65  12  12 0.00
Wed 08/19 12Z 0.15 2605  62  12  12 0.00
Wed 08/19 13Z 0.12 2504  58  20  12 0.00
Wed 08/19 14Z 0.16 2406  59  27  12 0.00
Wed 08/19 15Z 0.23 2408  61  30  12 0.00
Wed 08/19 16Z 0.24 2508  58  39  12 0.00
Wed 08/19 17Z 0.30 2508  55  53  12 0.00
Wed 08/19 18Z 0.34 2508  53  65  13 0.00
Wed 08/19 19Z 0.36 2608  56  68  13 0.00
Wed 08/19 20Z 0.46 2608  63  75  13 0.00
Wed 08/19 21Z 0.44 2508  70  76  13 0.00
Wed 08/19 22Z 0.49 2510  79  77  13 0.00
Wed 08/19 23Z 0.57 2513  86  74  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.54 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