NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260916_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)
=== ===== === ==== ==== === === === ====
Wed 09/16 12Z 0.30 2813  86  57  13 0.00
Wed 09/16 13Z 0.30 2813  89  51  13 0.00
Wed 09/16 14Z 0.27 2811  90  51  13 0.00
Wed 09/16 15Z 0.25 2810  91  60  13 0.00
Wed 09/16 16Z 0.25 2809  92  62  13 0.00
Wed 09/16 17Z 0.26 2709  94  63  13 0.00
Wed 09/16 18Z 0.28 2709  95  49  13 0.00
Wed 09/16 19Z 0.30 2708  94  47  13 0.00
Wed 09/16 20Z 0.32 2809  94  44  13 0.00
Wed 09/16 21Z 0.34 2810  94  37  13 0.00
Wed 09/16 22Z 0.33 2810  95  33  13 0.00
Wed 09/16 23Z 0.27 2808  95  29  13 0.00
Thu 09/17 00Z 0.27 2808  97  27  13 0.01
Thu 09/17 01Z 0.28 2809  97  25  13 0.01
Thu 09/17 02Z 0.23 2908  97  26  13 0.00
Thu 09/17 03Z 0.21 2808  97  27  13 0.00
Thu 09/17 04Z 0.16 2806  97  26  13 0.01
Thu 09/17 05Z 0.13 2804  97  23  13 0.01
Thu 09/17 06Z 0.12 2604  97  20  13 0.01
Thu 09/17 07Z 0.11 2403  97  17  13 0.01
Thu 09/17 08Z 0.12 2304  98  18  13 0.01
Thu 09/17 09Z 0.12 2305  99  20  13 0.01
Thu 09/17 10Z 0.14 2206 100  27  13 0.01
Thu 09/17 11Z 0.16 2108 100  27  13 0.01
Thu 09/17 12Z 0.20 2208 100  24  12 0.01
Thu 09/17 13Z 0.23 2209  99  29  12 0.01
Thu 09/17 14Z 0.26 2309  99  34  13 0.01
Thu 09/17 15Z 0.26 2409  99  32  13 0.01
Thu 09/17 16Z 0.27 2409  98  35  13 0.01
Thu 09/17 17Z 0.27 2409  97  41  13 0.00
Thu 09/17 18Z 0.29 2410  99  41  13 0.01
Thu 09/17 19Z 0.28 2409 100  55  13 0.02
Thu 09/17 20Z 0.22 2507  99  61  13 0.03
Thu 09/17 21Z 0.20 2606  99  88  13 0.05
Thu 09/17 22Z 0.17 2806  97  97  13 0.02
Thu 09/17 23Z 0.12 3005  91  95  13 0.03
Fri 09/18 00Z 0.11 2904  87  86  13 0.01
Fri 09/18 01Z 0.10 3005  87  76  13 0.00
Fri 09/18 02Z 0.12 3006  86  74  13 0.00
Fri 09/18 03Z 0.13 3007  82  78  13 0.00
Fri 09/18 04Z 0.14 3110  76  82  12 0.00
Fri 09/18 05Z 0.16 3112  66  84  12 0.00
Fri 09/18 06Z 0.14 3213  54  81  12 0.00
Fri 09/18 07Z 0.13 3215  49  87  12 0.00
Fri 09/18 08Z 0.11 3316  43  81  11 0.00
Fri 09/18 09Z 0.11 3319  49  82  10 0.00
Fri 09/18 10Z 0.12 3320  50  80  10 0.00
Fri 09/18 11Z 0.12 3321  55  55   9 0.00
Fri 09/18 12Z 0.14 3323  66  33   8 0.00
Fri 09/18 13Z 0.14 3323  74  22   7 0.00
Fri 09/18 14Z 0.15 3322  74  15   7 0.00
Fri 09/18 15Z 0.16 3321  74  11   6 0.00
Fri 09/18 16Z 0.35 3320  79   6   5 0.00
Fri 09/18 17Z 0.94 3219  84   2   5 0.00
Fri 09/18 18Z 0.94 3217  86   1   5 0.00
Fri 09/18 19Z 3.07 3218  82   2   5 0.00
Fri 09/18 20Z 3.28 3219  81   3   5 0.00
Fri 09/18 21Z 2.33 3220  78   3   5 0.00
Fri 09/18 22Z 0.80 3223  76   3   4 0.00
Fri 09/18 23Z 0.39 3325  71   3   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.32 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