Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260311_0600
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 03/11 06Z 0.05 2302  81  98   8 0.00
Wed 03/11 07Z 0.03 1704  86  98   8 0.01
Wed 03/11 08Z 0.03 1609  83  95   9 0.01
Wed 03/11 09Z 0.04 1616  80  96   9 0.00
Wed 03/11 10Z 0.08 1523  84  88   9 0.01
Wed 03/11 11Z 0.07 1629  85  74   9 0.00
Wed 03/11 12Z 0.06 1631  87  73   9 0.00
Wed 03/11 14Z 0.04 1732  84  89   9 0.03
Wed 03/11 15Z 0.08 1735  85  90   9 0.01
Wed 03/11 16Z 0.17 1833  92  92  10 0.01
Wed 03/11 17Z 0.20 1932  91  77  11 0.01
Wed 03/11 18Z 0.24 1933  91  50  11 0.01
Wed 03/11 19Z 0.23 1934  87  52  12 0.00
Wed 03/11 20Z 0.25 1936  85  44  12 0.00
Wed 03/11 21Z 0.28 1940  86  23  12 0.00
Wed 03/11 22Z 0.34 1942  89  35  12 0.00
Wed 03/11 23Z 0.35 1942  91  81  11 0.00
Thu 03/12 00Z 0.40 2044  90  86  12 0.01
Thu 03/12 01Z 0.51 2044  89  93  13 0.00
Thu 03/12 02Z 0.59 2143  92  86  12 0.00
Thu 03/12 03Z 0.72 2142  96  77  11 0.00
Thu 03/12 04Z 0.78 2144  98  84  12 0.00
Thu 03/12 05Z 0.99 2144  96  81  11 0.01
Thu 03/12 06Z 0.90 2235  98  72  11 0.06
Thu 03/12 07Z 1.21 2333  98  64   9 0.05
Thu 03/12 08Z 1.24 2530  98  75   7 0.07
Thu 03/12 09Z 0.90 2530  95  83   5 0.06
Thu 03/12 10Z 0.80 2630  94  80   1 0.04
Thu 03/12 11Z 0.85 2629  95  95  -2 0.03
Thu 03/12 12Z 0.76 2729  92  94  -4 0.04
Thu 03/12 13Z 0.87 2728  90  69  -6 0.03
Thu 03/12 14Z 0.86 2827  89  30  -8 0.01
Thu 03/12 15Z 1.09 2825  89  16 -10 0.00
Thu 03/12 16Z 2.66 2826  88   7 -11 0.00
Thu 03/12 17Z 5.60 2925  86   2 -11 0.00
Thu 03/12 18Z 5.86 2924  84   5 -11 0.00
Thu 03/12 19Z 4.98 2924  81   9 -11 0.00
Thu 03/12 20Z 2.98 3023  80  10 -11 0.00
Thu 03/12 21Z 1.24 3022  80  15 -11 0.00
Thu 03/12 22Z 1.10 3021  80  22 -11 0.00
Thu 03/12 23Z 0.94 3020  81  30 -11 0.00
Fri 03/13 00Z 1.02 3021  83  38 -11 0.00
Fri 03/13 01Z 1.37 2921  85  47 -11 0.00
Fri 03/13 02Z 1.43 2923  88  52 -12 0.00
Fri 03/13 03Z 1.50 2923  91  53 -12 0.00
Fri 03/13 04Z 1.53 2923  92  56 -12 0.00
Fri 03/13 05Z 1.01 3023  92  59 -12 0.00
Fri 03/13 06Z 0.82 3021  92  57 -12 0.00
Fri 03/13 07Z 0.82 2920  94  56 -12 0.00
Fri 03/13 08Z 0.72 2917  93  45 -12 0.00
Fri 03/13 09Z 0.63 2816  92  30 -12 0.00
Fri 03/13 10Z 0.65 2716  92  20 -12 0.00
Fri 03/13 11Z 0.52 2714  91  10 -11 0.00
Fri 03/13 12Z 0.29 2509  84   5 -10 0.00
Fri 03/13 13Z 0.25 2309  78   6 -10 0.00
Fri 03/13 14Z 0.20 2109  69   6  -9 0.00
Fri 03/13 15Z 0.16 1911  59   8  -9 0.00
Fri 03/13 16Z 0.19 1814  55  24  -9 0.00
Fri 03/13 17Z 0.87 1816  57  54  -9 0.00

Run total areal avg QPF for the Central_Greens is: 0.51 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