NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260906_1800
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)
=== ===== === ==== ==== === === === ====
Sun 09/06 18Z 0.20 3410  92  62   7 0.00
Sun 09/06 19Z 0.21 3313  92  52   7 0.01
Sun 09/06 20Z 0.11 3416  89  37   7 0.01
Sun 09/06 21Z 0.07 3417  86  26   7 0.00
Sun 09/06 22Z 0.05 3517  84  13   7 0.00
Sun 09/06 23Z 0.05 3518  84   7   7 0.00
Mon 09/07 00Z 0.09 3520  84  10   7 0.00
Mon 09/07 01Z 0.11 3521  84  13   7 0.00
Mon 09/07 02Z 0.09 3522  86  11   7 0.00
Mon 09/07 03Z 0.06 3521  86  11   6 0.00
Mon 09/07 04Z 0.06 3521  83  14   7 0.00
Mon 09/07 05Z 0.04 3421  82  13   6 0.00
Mon 09/07 06Z 0.06 3420  83  13   6 0.00
Mon 09/07 07Z 0.04 3419  80  13   7 0.00
Mon 09/07 08Z 0.07 3418  77  15   7 0.00
Mon 09/07 09Z 0.11 3419  73  17   7 0.00
Mon 09/07 10Z 0.18 3320  71  18   7 0.00
Mon 09/07 11Z 0.21 3321  69  21   7 0.00
Mon 09/07 12Z 0.15 3423  66  30   7 0.00
Mon 09/07 13Z 0.17 3424  68  31   7 0.00
Mon 09/07 14Z 0.16 3423  71  29   7 0.00
Mon 09/07 15Z 0.12 3421  71  27   8 0.00
Mon 09/07 16Z 0.54 3419  73  19   8 0.00
Mon 09/07 17Z 1.46 3317  75  12   8 0.00
Mon 09/07 18Z 2.44 3317  74  10   8 0.00
Mon 09/07 19Z 2.79 3317  72  10   8 0.00
Mon 09/07 20Z 2.49 3217  70   7   9 0.00
Mon 09/07 21Z 2.38 3217  73   5   9 0.00
Mon 09/07 22Z 1.46 3218  78   4   8 0.00
Mon 09/07 23Z 1.01 3218  77   7   8 0.00
Tue 09/08 00Z 0.86 3219  79  10   8 0.00
Tue 09/08 01Z 0.54 3219  81  18   8 0.00
Tue 09/08 02Z 0.37 3219  80  26   9 0.00
Tue 09/08 03Z 0.28 3219  78  40   9 0.00
Tue 09/08 04Z 0.26 3219  76  52  10 0.00
Tue 09/08 05Z 0.22 3220  77  67  10 0.00
Tue 09/08 06Z 0.21 3218  76  62  10 0.00
Tue 09/08 07Z 0.21 3218  79  70  10 0.00
Tue 09/08 08Z 0.23 3216  80  59   9 0.00
Tue 09/08 09Z 0.29 3218  85  68   9 0.00
Tue 09/08 10Z 0.28 3218  87  69   9 0.00
Tue 09/08 11Z 0.33 3119  89  65   9 0.00
Tue 09/08 12Z 0.36 3120  93  64   9 0.00
Tue 09/08 13Z 0.32 3119  94  65   9 0.01
Tue 09/08 14Z 0.29 3219  95  44   9 0.01
Tue 09/08 15Z 0.23 3217  94  18   9 0.00
Tue 09/08 16Z 0.20 3216  91   4   9 0.00
Tue 09/08 17Z 0.17 3316  85   3  10 0.00
Tue 09/08 18Z 0.14 3314  78   4  10 0.00
Tue 09/08 19Z 0.19 3213  72   4  10 0.00
Tue 09/08 20Z 0.18 3212  66   3  10 0.00
Tue 09/08 21Z 0.16 3211  57   3  11 0.00
Tue 09/08 22Z 0.13 3209  50   3  11 0.00
Tue 09/08 23Z 0.14 3209  44   8  11 0.00
Wed 09/09 00Z 0.14 3108  43  34  11 0.00
Wed 09/09 01Z 0.18 3008  55  57  11 0.00
Wed 09/09 02Z 0.19 3008  70  86  11 0.00
Wed 09/09 03Z 0.17 2906  73  84  11 0.00
Wed 09/09 04Z 0.16 2605  69  79  12 0.00
Wed 09/09 05Z 0.19 2606  74  75  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.04 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