Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260310_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)
=== ===== === ==== ==== === === === ====
Tue 03/10 12Z 0.57 2619  47  42   8 0.00
Tue 03/10 13Z 0.57 2619  46  41   8 0.00
Tue 03/10 14Z 0.57 2519  46  43   8 0.00
Tue 03/10 15Z 0.57 2518  48  47   8 0.00
Tue 03/10 16Z 0.56 2417  49  43   8 0.00
Tue 03/10 17Z 0.61 2416  49  43   8 0.00
Tue 03/10 18Z 0.66 2316  49  40   8 0.00
Tue 03/10 19Z 0.75 2318  50  46   8 0.00
Tue 03/10 20Z 0.87 2419  56  43   8 0.00
Tue 03/10 21Z 0.95 2520  67  41   8 0.00
Tue 03/10 22Z 0.99 2622  78  40   7 0.00
Tue 03/10 23Z 0.78 2621  87  40   7 0.01
Wed 03/11 00Z 0.60 2719  91  40   7 0.01
Wed 03/11 01Z 0.46 2716  93  42   7 0.00
Wed 03/11 02Z 0.36 2714  95  38   7 0.00
Wed 03/11 03Z 0.29 2712  97  41   7 0.00
Wed 03/11 04Z 0.24 2710  97  47   7 0.00
Wed 03/11 05Z 0.17 2607  98  83   7 0.00
Wed 03/11 06Z 0.11 2306  99  83   8 0.01
Wed 03/11 07Z 0.08 2007  99  84   8 0.01
Wed 03/11 08Z 0.06 1812  99  85   8 0.01
Wed 03/11 09Z 0.02 1717  99  86   8 0.03
Wed 03/11 10Z 0.03 1622  98  72   8 0.03
Wed 03/11 11Z 0.04 1627  98  55   8 0.03
Wed 03/11 12Z 0.03 1729  98  38   8 0.03
Wed 03/11 13Z 0.07 1730  98  38   9 0.03
Wed 03/11 14Z 0.11 1832  98  44   9 0.03
Wed 03/11 15Z 0.14 1833  97  56  10 0.03
Wed 03/11 16Z 0.18 1834  95  66   9 0.03
Wed 03/11 17Z 0.20 1935  94  41   9 0.01
Wed 03/11 18Z 0.20 1936  94  27   9 0.01
Wed 03/11 19Z 0.21 1937  94  55  10 0.01
Wed 03/11 20Z 0.24 1937  94  70  11 0.01
Wed 03/11 21Z 0.26 1939  93  86  11 0.01
Wed 03/11 22Z 0.29 1941  91  83  12 0.00
Wed 03/11 23Z 0.32 1941  96  90  11 0.03
Thu 03/12 00Z 0.36 2041  94  95  11 0.02
Thu 03/12 01Z 0.48 2041  95  87  11 0.01
Thu 03/12 02Z 0.59 2145  96  91  12 0.01
Thu 03/12 03Z 0.63 2046  96  77  12 0.02
Thu 03/12 04Z 0.77 2044  98  90  11 0.05
Thu 03/12 05Z 1.25 2336  98  58   9 0.09
Thu 03/12 06Z 1.21 2437  97  51   9 0.02
Thu 03/12 07Z 1.38 2434  99  74   7 0.04
Thu 03/12 08Z 1.29 2536  96  57   0 0.07
Thu 03/12 09Z 1.83 2639  89  30  -4 0.03
Thu 03/12 10Z 2.92 2637  87  17  -8 0.00
Thu 03/12 11Z 2.30 2636  92   3 -10 0.00
Thu 03/12 12Z 2.12 2638  94   1 -11 0.00
Thu 03/12 13Z 8.02 2738  91   3 -12 0.01
Thu 03/12 14Z 15.15 2738  86   8 -13 0.00
Thu 03/12 15Z 14.52 2735  86  12 -12 0.00
Thu 03/12 16Z 17.91 2832  86  17 -12 0.00
Thu 03/12 17Z 16.36 2829  78  22 -12 0.00
Thu 03/12 18Z 17.04 2827  74  28 -12 0.00
Thu 03/12 19Z 15.67 2826  70  38 -11 0.00
Thu 03/12 20Z 16.50 2826  72  41 -11 0.00
Thu 03/12 21Z 15.02 2825  76  44 -11 0.00
Thu 03/12 22Z 8.36 2824  82  49 -11 0.00
Thu 03/12 23Z 2.90 2824  86  56 -11 0.00

Run total areal avg QPF for the Central_Greens is: 0.74 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